# How To Work With Forms in React

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• by Abhresh S
• 13th May, 2021
• Last updated on 13th May, 2021

Forms are a crucial part of React web applications. They allow users to enter and upload information directly in components from a login screen to a checkout page. As the majority of React applications are single-page apps or web apps that load one page dynamically displaying new information, you will not send the information to a server directly from the form. You will instead capture and submit or show the information in the form on the client-side using an additional JavaScript file.

Reactforms are unique because either you can allow the browser to process and collect data through React Change Events, or you can use React to completely manage this feature by setting and modifying its input value directly. React formats are unique because they can be reused. The first approachis an unregulated component because React does not set the value. The second approach is a controlled component, since React updates the inputs actively.

## Handling Forms

Form handling is an important part of a wide variety of internet applications and React is one of the best way to handle forms. You have plenty of flexibility to regulate and enforce these controls and there are many ways to accomplish the same.

HTML form components function a little differently than the other DOM components, as form components naturally hold some internal status.

When the user submits the form, the Form is the default HTML form browsing activity for a new page. In react, it works only if you want this behaviour. In most cases, however, it is advisable to have a JavaScript function which handles the form submission and has access to the form's user data. A technique called 'controlled components' is the traditional way to do this.

## Controlled Components

A controlled component is bound to a value, and its adjustments will be handled in code by using event-based callbacks. Here, the input form variable is handled by the react itself rather than the DOM. In this case, the mutable state is maintained in the state property and modified using setState().

Controlled components have functions which regulate the data that occurs at each on Change event. This data is subsequently saved in the setState() method and updated. It helps components manage the elements and data of the form easier.

The controlled component is a way you can handle the form input via state. If you are using React Hooks, you can change the form input value by just one way and when the user begins writing some setState or useState characters, this state can be called and you can update it through one event like on Change.

You can use the controlled component when you create:

• Forms validation so that when you type, you always have to know the input value to verify whether it is true or not!
• Disable submission icon, except for valid data in all fields
• If you have a format such as the input for a credit card.

## Conditional Rendering

You can create dynamic, highly interactive single-page applications (SPAs). The conditional rendering is one function that enables this.

Conditional rendering is a concept that defines how various user interface markups can be rendered if a condition istrue or false. In response, it enables us to make various elements or components dependent on a condition. In the following scenarios this concept is used:

• External API data rendering
• Elements may be shown or hidden
• The functionality of the toggling application
• Permit level implementation
• Authentication and approval management.

## Submitting Forms

Our new item has additional features, so we have to add additional fields to accommodate these features. We also need to establish a feature to fire the form and transmit information to the remote collection so that it can also be applied.

To call handleSubmit, we must add it to the onSubmit prop on the form. OnSubmitwatches and invokes the features to which we transfer them for the form submits.

handleFormSubmit = (event) => {
console.log(this.state.name)
event.preventDefault();
};
render() {
return (
<form onSubmit={this.handleFormSubmit}>
<label>Name:</label>
<input type="text" value={this.state.name} onChange={this.handleNameChange} />
<button type="submit">Send</button>
</form>
);
} 

## Multiple Input Fields

It is normal to use an onChange handler to listen to changes in the input elements and save their values to form when building a form using react components. A single onChange handler can be configured to manage several different inputs in the form, in addition to managing just one input.

render() {
const colors = ['Blue', 'Red', 'Green', 'Yellow'];
const sizes = ['Small', 'Medium', 'Large', 'XL', 'XXL', '3XL'];
return (
<form>
<ul>
<li>
<label>Name:</label>
<input name="name" type="text" value={this.state.name} onChange={this.handleChanges} />
</li>
<li>
<label>Observation:</label>
<textarea name="observation" value={this.state.observation} onChange={this.handleChanges} />
</li>
<li>
<label>Desired color:</label>
<select name="color" value={this.state.color} onChange={this.handleChanges}>
{colors.map((color, i) => <option key={i} value={color.toLowerCase()}>{color}</option>)}
</select>
</li>
<li>
<label>T-shirt Size:</label>
{sizes.map((size, i) =>
<label key={i}>
{size}
<input
name="size"
value={size.toUpperCase()}
checked={this.state.size === size.toUpperCase()}
onChange={this.handleChanges}
</label>
)}
</li>
<li>
<label>
I accept the agreement
<input name="acceptedAgreement" type="checkbox" value={this.state.acceptAgreement} onChange={this.handleChanges} />
</label>
</li>
</ul>
</form>
);
} 

## Validating Form Input

The form must also be able to accept values so that both a development and an edit flow can be used. Since both forms of validation wish to use the same form component, the State and validation logic shall be lifted to a parent component to carry out the validation.

Example:

<form>
</form>

We have just added a required input feature. In case an empty and valid field has at least one character, the browser will find this input field invalid. If the input fields are at least invalid, the browser will not allow the user to send the form.

To show input error feedback we need to transfer the affected and correct properties to its component as a prop for that particular input. Based on the valid state, we will add the error style. We need to update our component file.

import React from 'react';
const TextInput = props => {
let formControl = "form-control";
if (props.touched && !props.valid) {
formControl = 'form-control control-error';
}
return (
<div className="form-group">
<input type="text" className={formControl} {...props} />
</div>
);
}
export default TextInput; 

## The textarea Tag

Textarea, which is used to get multi-line feedback from the user, is a popular form control. It’s different from a standard text entry that only allows one-line input. An address field is a clear example of a Textarea use case.

Example:

export default class App extends Component {
state = { bio: '' };

handleBioChange = (e) => {
const bio = e.target.value;
this.setState({ bio });
};

render() {
return (
<form>
<label>Bio:</label>
<textarea value={this.state.bio} onChange={this.handleBioChange} />
</form>
);
}
} 

## The select Tag

Select inHTML helps us to use the dropdown for choosing among many values. Here we are addressing adjusting selected choices based on a particular dropdown. In React, with the aid of the State it is very simple to achieve. Its a brief for those who dont care about state.

render() {
return (
<form>
<label>Desired color:</label>
<select value={this.state.color} onChange={this.handleColorChange}>
<option></option>
<option value="orange">Blue</option>
<option value="red">Red</option>
<option value="green">Green</option>
<option value="yellow">Yellow</option>
</select>
</form>
);
} 

## The file input Tag

In HTML, the user can upload or manipulate one or more files of the device’s storage via the File API via JavaScript.

<input type="file" />

We generate a component of FileUpload and save the file object. We get the uploaded picture file via event.target, update the component status, and show the picture and information.

## Handling Multiple Inputs

You can add a name attribute to each item when you need to handle several managed input items.

function useFormFields<T>(initialValues: T) {
const [formFields, setFormFields] = React.useState<T>(initialValues);
const createChangeHandler = (key: keyof T) => (
e: React.ChangeEvent<HTMLInputElement>,
) => {
const value = e.target.value;
setFormFields((prev: T) => ({ ...prev, [key]: value }));
};
return { formFields, createChangeHandler };
}

const { formFields, createChangeHandler } = useFormFields({
email: "",
}); 

## Controlled Input Null Value

The value change of a controlled component prevents the user from adjusting the input unless you wish to. You can accidentally set the value as undefined or null if you have specified a value, but the input is still editable.

class ControlledInput extends React.Component {
constructor(props) {
super(props);
this.state = { name: '' };
this.handleInput = this.handleInput.bind(this);
}

handleInput(event) {
this.setState({
name: event.target.value
});
}

render() {
return (
<input type="text" value={this.state.name} onChange={this.handleInput} />
);
}
} 

## Alternatives to Controlled Components

It is often tedious to use controlled components, because for every manner in which your data modifies and pipes the entire input state using a Reactcomponent, you will need to create an Event Handler.

export function LoginForm() {
const handleSubmit = (e: React.FormEvent) => {
e.preventDefault();
const formData = new FormData(e.target as HTMLFormElement);
};
return (
<form onSubmit={handleSubmit}>
<div>
<label htmlFor="email">Email</label>
<input
type="email"
id="email"
name="email"
/>
</div>
<div> 

Perhaps you found that in the handleSubmitfunctionwe are doing something new. We use an integrated FormData browser API. FormData is a convenient way to get field values from our fields of input!

## Creating a Basic Form with JSX

With a single element and a submit button using JSX, you are going to generate an empty form. You will manage the form and transfer the information to another service.

import React from 'react';
import './App.css';
function App() {
return(
<div className="wrapper">
<form>
<fieldset>
<label>
<p>Name</p>
<input name="name" />
</label>
</fieldset>
<button type="submit">Submit</button>
</form>
</div>
)
}
export default App; 

## Collecting Form Data Using Uncontrolled Components

In this stage, uncontrolled components will be used to collect form data. An uncontrolled component is acomponent with no response meaning. You can bind to the onChange event to collect the user feedback instead of setting the data on the component. You can learn how the react handles various types of input and how you construct a reusable feature for collecting form data into a single object as you develop the components.

import React, { useReducer, useState } from 'react';
import './App.css';
const formReducer = (state, event) => {<^>
return {
...state,
[event.name]: event.value
}
}
function App() {
const [formData, setFormData] = useReducer(formReducer, {});
const [submitting, setSubmitting] = useState(false);

const handleSubmit = event => {
event.preventDefault();
setSubmitting(true);

setTimeout(() => {
setSubmitting(false);
}, 3000);
}

const handleChange = event => {
setFormData({
name: event.target.name,
value: event.target.value,
});
}

return(
<div className="wrapper">
{submitting &&
<div>Submtting Form...</div>
}
<form onSubmit={handleSubmit}>
<fieldset>
<label>
<p>Name</p>
<input name="name" onChange={handleChange}/>
</label>
</fieldset>
<button type="submit">Submit</button>
</form>
</div>
)
}
export default App; 

## Updating Form Data Using Controlled Components

You’ll set up and update your data dynamically with controlled components in this phase. To set or update the form data, you can add a value prop for each variable. The form data will also be reset on the submit.

...
return(
<div className="wrapper">
{submitting &&
<div>
You are submitting the following:
<ul>
{Object.entries(formData).map(([name, value]) => (
<li key={name}><strong>{name}</strong>: {value.toString()}</li>
))}
</ul>
</div>
}
<form onSubmit={handleSubmit}>
<fieldset>
<label>
<p>Name</p>
<input name="name" onChange={handleChange} value={formData.name || ''}/>
</label>
</fieldset>
<fieldset>
<label>
<p>Apples</p>
<select name="apple" onChange={handleChange} value={formData.apple || ''}>
<option value="fuji">Fuji</option>
<option value="jonathan">Jonathan</option>
<option value="honey-crisp">Honey Crisp</option>
</select>
</label>
<label>
<p>Count</p>
<input type="number" name="count" onChange={handleChange} step="1" value={formData.count || ''}/>
</label>
<label>
</label>
</fieldset>
<button type="submit">Submit</button>
</form>
</div>
)
}

export default App; 

## Dynamically Updating Form Properties

You will update the form element properties dynamically in this process. During the submission, you can set the property to previous choices to avoid unintended submissions and disable your form.

Every part is currently static. It does not shift with the shape changing. Forms are complex in many applications. Based on previous data, fields can change, justify and reveal mistakes. Fields may disappear or grow as other components are filled.

Like most React components, the components and attributes can be dynamically defined and re-rendered with changes in data.

## Fully-Fledged Solutions

Formik is one of the most common options if you’re looking for a full solution, including validation, monitoring of the fields visited, and submitting a handling form. However, it is based on the same controlled components and state management principles—so it is important to get to know them.

Conclusion

In-depth knowledge of forms is important for rich Web apps. In React, you have different options for forms and elements to be connected and regulated. You can upgrade properties, including the value input elements, dynamically like other components. The best way of simplifying unchecked components is to clean them or trigger them with data, but they may not be appropriate circumstances. You can also change data by using controlledcomponents, but can add another abstraction level which can trigger unintended bugs or re-renders.

### Abhresh S

Author

An Online Technical Trainer by profession! And Content writer by hobby! Interested in sharing quality knowledge to make the Industry grow better towards better success and better tomorrow! With a Guru Mantra of - "Keep Learning & Keep Practicing".

## Back Up, Restore, and Migrate a MongoDB Database

Popular among both enterprises and startups, MongoDB is a database that is perfectly suited for web-apps that need to scale once the user base increases. MongoDB is different from traditional relational databases because it uses json like objects to store data, instead of tables in relational databases. In this post, we will learn to backup and restore a MongoDB database. In all software products there is an import and export feature, which in database terms, deals with human-readable format. On the other hand, the backup and restore operations use MongoDB specific data, which preserve the MongoDB attributes.  So, when migrating the database, we should prefer backup and restore over import and export. But we should also keep in mind that our source and target systems are compatible, which means that both should be Windows or both should be a Linux based system like Ubuntu/Mac. Prerequisites We are using Windows 10 in this tutorial. Please make sure you have downloaded the MongoDB Community Server and installed in it. It is a very easy setup and you will find lot of good articles on the internet detailing this out. Please ensure that you have added it in the Environment variable in your PC. Backup Considerations In a production environment, backups act as a snapshot of the database at a certain point. Large and complex databases do fail or can be hacked. If that happens, we can use the last backup file to restore the database to the point, before it failed. These are some of the factors which should be taken into consideration when doing a recovery.  1. Recovery Point Objective We should know the objective of the recovery point, which means how much data we are willing to lose during a backup and restoration. A continuous backup is preferred for critical data like bank information and backups should be taken several times during the day. On the other hand, if the data doesn’t change frequently, then the backup can be taken every 6 months.  2. Recovery Time ObjectiveThis tells how quickly the restoration can be done. During restoration the application will be down for some time; and this downtime should be minimized, or else customer relationships will be lost.  3. Database and Snapshot IsolationThis refers to the distance between the primary database server and the backup server. If they are close enough i.e., in the same building, then the recovery time reduces. However, in the event of a physical event such as a fire, there is a likelihood of it been destroyed with the primary database.   4. Restoration Process We should always test our backups in test servers to see if they will work, in case a restoration is required.  5. Available Storage Backup of database generally takes a lot of space and in most cases, it will never be required. So, we should try to minimize the space taken on the disk, by archiving the database into a zip file.  6. Complexity of DeploymentThe backup strategy should be easy to set and should be automated, so that we don’t have to remember to take the backup after regular intervals. Understanding the Basics The first thing that we should know is that MongoDB uses json and bson(binary json) formats for storing data. So, people coming from a JavaScript background can relate to objects for json, which have a key-value pair. Also, json is the preferred format in which we receive or send data to an API endpoint. You can check the json data of a MongoDB database in any tool or online editors. Even the famous Windows application Notepad++ has a json viewer. An example of a json document looks like below. As we can see from the above example, json is very convenient to work with, especially for developers.  But it doesn’t support all the data types available in bson. So, for backup and restoring, we should use binary bson. The second thing to keep in mind is that MongoDB automatically creates databases and collection names if they don’t exist during restore operations. Third, since MongoDB is a document-based database, in many user cases we store large amounts of data in one collection, such as the whole post of an article. MongoDB is also used extensively in large databases and big data. So, reading and inserting the data can consume a lot of CPU, memory and disk space. We should always run the backups during the non-peak hours like night. As already mentioned earlier, we can use import and export functions for backup and restoration of MongoDB databases, but we should use commands like mongodump and mongorestore to backup and restore respectively. MongoDB backup We will first cover backing up the MongoDB database. For this we use the mongodump command.  First open the Windows command prompt and go to the location in which MongoDB is installed. If you have chosen the default setting, while installing MongoDB though the pop-up it will be installed in a location like C:\Program Files\MongoDB\Server\4.4\bin The version number only will change if you are reading this blog in the future. Also, note that it’s better to run the command prompt in the Admin mode. So, once we open the command prompt, we need to change the directory to MongoDB bin folder by giving the below command. cd C:\Program Files\MongoDB\Server\4.4\binNow, enter mongod and press enter. It will show some json text.Now, we can backup to any location. For this post I am backing up on my Desktop in a Backup folder, which I have created through the command line.Now, we have to run mongodump command, but it should be also present in our MongoDB bin folder. If it is not present, we need to download it from and install it. After this, copy the entire exe files from the download to the MongoDB bin folder. MongoDB Backup with no option Now, run the mongodump command from the bin directory. Here, we are not giving any argument so the backup of the whole database will be taken in the same bin directory.MongoDB Backup to an output directory Now, run the mongodump command from the bin directory. Here, the argument –out specifies the directory in which the data backup will be maintained. In our case we are giving the Backup folder in the  Desktop, which we have created earlier. mongodump --out C:\Users\pc\Desktop\Backup Now, go to the desktop and you can find the backup that has been created in our Backup folder.  MongoDB Backup a specific database Now, we can also backup only a database in mongodump using the –db option. I have an example database, so to backup only that I will use the below command. mongodump --db example --out C:\Users\pc\Desktop\Backup As, you can see in the below output only the example database was backed up. MongoDB Backup a specific collection Now, if we want to only backup a specific collection, we need to use the –collection option and give the collection name. Also, note that the database name is mandatory in this case, as mongodb needs to know about the database to search for the collection. I have a products collection within the example database, so to backup only that I will use the below command. mongodump --db example --out C:\Users\pc\Desktop\Backup –collection products As, you can see in the below output only the products collection from example database was backed up. MongoDB Backup from remote MongoDB instances We can get the backup from remote mongodb instances also. I have a lot of MongoDB databases for my personal projects on MongoDB atlas, which is the free to use Cloud database for MongoDB. To get a backup of remote databases, we have to use the connection string with –uri parameter. I used the below command. mongodump --uri "mongodb+srv://xxxx:xxxxxxxxxxx@cluster0.suvl2.mongodb.net/xxxxxDB?retryWrites=true&w=majority" --out C:\Users\pc\Desktop\Backup You can see in the below output the backup of the remote instance. MongoDB Backup procedures We should try to make the backup procedure as automated as possible. One of the best ways is to use a cron job, so that it can run every day. As, discussed earlier it is best to run the backup in the night when the database has the least load.  Setting up a cron job is easier on a Linux or a Mac because the Windows equivalent of it is not good. Alternatively, you can do install mongodb in WSL2 for Windows which supports Ubuntu.  Suppose, on a Linux host which has a mongoDB instance running, you want to run the backup at 04:04 am daily. For this in the terminal, open the cron editor by running the below command in the terminal. sudo crontab –e Now, in the cron editor, you need to add a command like below for our case. 4 4 * * * mongodump --out /var/backups/mongobackups/date +"%m-%d-%y"Restoring and migrating a MongoDB database When we restore the MongoDB database from a backup, we will be able to take the exact copy of the MongoDB information, including the indexes. We restore MongoDB by using the command mongorestore, which works only with the binary backup produced by mongodump. Now, we have taken the backup of example database earlier and it is in our Backup folder. We will use the below command to restore it. In the arguments we will specify the name of the database first with –db option. After that with –drop, we make sure that the example database is first dropped. And in the final argument, we specify the path of our backup. mongorestore --db example --drop C:\Users\pc\Desktop\Backup\example Now, if we check in terminal, we have our example database restored properly. Conclusion In this article, we have learned about MongoDB backup and restore. We have learned the different options for the backups, and why and when backups are required. Keep learning!
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Back Up, Restore, and Migrate a MongoDB Database

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## How to Work With Forms In JavaScript

Forms also referred as web forms are a very important part of front end web application development for sake of interaction with users. Most commonly, forms are used to collect the data from users or provide a provision for user to control the user interface. Forms are great potential assets if correctly used in building an interactive web application. We would be touch basing some of the essential aspects of them like HTML structure, styling form controls, events, data validation and submitting data to server.Understanding forms in detail needs expertise in other areas than just HTML like styling form controls (CSS), scripting to validate or create custom controls (JavaScript).We would be referring or using libraries like Jquery (for document traversal, manipulation etc) and parsley (form validation library) to build better forms.A typical form’s HTML is made of HTML elements called as form controls like single or multiline text fields, dropdowns, checkboxes, button etc mostly created using element with specific type being set on Type attribute. These form controls can be programmed to add some validations to support specific values based on constraints set on them. These controls can be enriched to support accessibility for enabling the interaction for less privileged users.Let’s create a simple html page to build a form.           Learning Forms       All forms have to start with element which is container having the form fields user would interact with. All attributes of element are optional but for programming forms to capture data we need at least ‘action’ and ‘method’ attributes.action – is basically the URL where the form fields data would be sent to.method – corresponds to the HTTP method to submit the form data. Possible HTTP method names which can be set as values are post and get. And another value dialog is set when form is imbedded inside a .Note: Both formaction and formmethod can be overridden by button, input with type submit elements which we will learn as we go forward.Refer to this link to know more about form attributes.Let’s add a form element to our body with action (“”) and method(“get”). This implies that form will send a GET request to the current URL. If it is post then it would be a POST request to the URL in action. Add few fields to form say name, email and a submit button using with type being specified as text, email and submit respectively.Note: The tag is an empty element, meaning that it doesn't need a closing tag. Value attribute can be populated to set the default value.          Enter your name:                    Enter your email:                       Save and open the html in chrome or your preferred browser. Clicking on ‘Click me!’ should send a http get call with empty name and email.Note: We can use instead of with type as submit. The difference is that button can contain HTML content allowing to create a complex button whereas input allows only plain text.Let’s understand the Sending of form data.If we observer all the form fields again, we have added an attribute called ‘name’. This property is important to inform that which data is associated with which form field i.e. name/value pairs. Try adding some data to our fields rendering in html (say myName and first.last@email.com) and click submit button. You should see the data being sent as query parameters in the browser URL.?name=myName&email=first.last@email.com.Change the Form method value to POST instead of GET and send the submitted data by clicking the ‘Click me!’ button. You should be seeing Form Data being sent but the browser URL will not get update.name: myName email: first.last@email.comAll this while, we have our action method being set as empty. Replace this with another URL on server side say ‘/captureFormData’. Now on clicking submit button the data should be received by the script at ‘/captureFormData’ with key/value items contained in the HTTP request object.Note that each server-side language like Node.js, C# etc have their own way of handling the submitted form data. And this blog would not cover those topics and it is beyond the scope.Let’s refine our basic form structure with help of other HTML elements like , , etc. Though we used few of them in basic example. Let’s go little deep on them.Note: Nesting of form inside another form is unacceptable as it might result in unpredictable behavior. is a convenient way of grouping for sake of styling and semantic purpose. This control can be associated with so that some assistive technologies can read this legend and associate it with the controls inside the . Let’s understand this will an example:         Interested programming language                             JavaScript                                     CSharp                                     Java               When reading the above form by any screen readers, it will read as “Interested programming language JavaScript” for the first radio, “Interested programming language CSharp” and “Interested programming language Java” for second and third radio.Imagine if you have a long form with multiple fields. It would help to improve the usability if we can categorize/section them with the help of . It would even help to improve the accessibility of forms.Talking about accessibility, with the associated correctly with the via its for attribute (which contains the element's id attribute), a screenreader will read out something like "name, edit text" for below one.Enter your name: Another advantage of having label associated with input of type text, radio etc is they are clickable too.  If you click on a label then the associated input control will get the focus. If the input control is of type checkbox or radio, clicking on label will select the check box and radio. This will be useful as clickable area of checkbox or radio is small and having label gives provision to select it easily.Note: We can always associate multiple labels to a single input control but it is not a good idea as it will impact the accessibility and assistive technologies. along with can be used to separate the functionality in a form and group the same purpose elements like radio buttons.Here is an example of the same.               Contact information                   Title                                                                             Mr                                                                                                 Mrs                                                                               Name:                                                           E-mail:                                                           Password:                                                 Additional information                               Social type:                                 LinkedIn             Twitter             Instagram                                                 Phone number:                                                           Submit                   Every time you like to create an HTML form you need to start using element and  nesting all the content controls inside it. Most of the assistive technologies and browser plugins can help to discover elements and implement special hooks to make them easier to use.We have already some of the form elements like , , , , , and . Other common input types are button, checkbox, file, hidden, image, password, radio, reset, submit, and text.Input types.Attributes of Input.Few attributes on element help in validating the data like required, max, maxlength, min, minlength, multiple, pattern, step etc based on their respective type.Also other attributes on of type submit/image like formaction, formmethod, formnovalidate, formenctype etc helps in overriding the form level methods.ValidationBefore submitting the data to the server, it is important to perform some client side validation to avoid unwanted round trips. Client-side validation is needed but it is not a replacement to the server side validation. Advantage of having client side validation is to capture the invalid data and fix it immediately.Some of the important and popular checks which are most commonly used on client areField requiredSpecific data formatEnter valid email addressPassword and more…Let’s build a form with the above validation checks.                         Do you have experience in programming ?*                     Yes           No                             How many years of experience you have ?                                     What's your programming language?*                           TypeScript           Java           CSharp           Ruby           Go           Swift                             What's your company e-mail address?                             Cover letter                             Submit       Say, if we enter an value which is more than 40 in experience field. We should see an inbuilt error as shown below:All these validations and notifications are coming out of the box. Thanks to inbuilt functionality in control. Let’s see how we can perform validation of forms using JavaScript and take control of look and feel of error message.Most browsers support constraint validation API by providing few validation properties on HTML elements like , , , etc.validationMessage: we can customize this message if the control value failed validation otherwise it will return an empty string. It is dependent on other constraint i.e. willValidate and isValid.willValidate: If element is validated then it will be true otherwise false.validity: is the validity state of the element and it is dependent on other properties likepatternMatch for specified pattern attribute,tooLong and tooShort are for string fields based on maxLength and minLengthrangeOverflow and rangeUnderflow for numeric fields based on max and min attributestypeMatch for fields which are based on email or url.valid if all the validation constraints are metvalueMissing if the field is set as required.Along with properties, we do also have methods to perform validation like checkValidity() which returns true or false and setCustomValidity(message) is to set the message if the element is considered invalid. Also if the element is invalid then checkValidity will raise an event called invalid Event.Let’s create a simple form and customize the validation message.       Please enter an email address:             Submit     Add a script tag and customize the message as shown below:     const email = document.getElementById("mail");     email.addEventListener("input", function (event) {       if (email.validity.typeMismatch) {         email.setCustomValidity("I am expecting an e-mail address!");       } else {         email.setCustomValidity("");       }     });   Here we are listening to the input event on email field and checking if the validity on the control is valid or not and based on that we are setting the custom message.Here are we relying on inbuilt validation method. Let’s disable the validation at form level by with the help of ‘novalidate’ and take control over validation. This would mean the browser will not perform auto check on validation before sending the data. But still we have access to constraint validation API to perform validation ourself.Refine the above form to add few addition validation like required and minLength etc.               Please enter an email address:                             Submit     Let’s update the script to handle the validation     const form  = document.getElementsByTagName('form')[0];     const email = document.getElementById('mail');     const emailError = document.querySelector('#mail + span.error');     email.addEventListener('input', function (event) {       // Each time the user types something, we check if the form fields are valid.       if (email.validity.valid) {         // In case there is an error message visible, if the field is valid, we remove the error message.         emailError.textContent = ''; // Reset the content of the message         emailError.className = 'error'; // Reset the visual state of the message       } else {         // If there is still an error, show the correct error         showError();       }     });     form.addEventListener('submit', function (event) {       // if the email field is valid, we let the form submit       if(!email.validity.valid) {         // If it isn't, we display an appropriate error message         showError();         // Then we prevent the form from being sent by cancelling the event         event.preventDefault();       }     });     function showError() {       if(email.validity.valueMissing) {         // If the field is empty display the following error message.         emailError.textContent = 'You need to enter an e-mail address.';       } else if(email.validity.typeMismatch) {         // If the field doesn't contain an email address display the following error message.         emailError.textContent = 'Invalid value is entered, expected an e-mail address.';       } else if(email.validity.tooShort) {         // If the data is too short display the following error message.         emailError.textContent = Email should be at least ${ email.minLength } characters; you entered${ email.value.length }.;       }       // Set the styling appropriately       emailError.className = 'error active';     } Reload the HTML and try entering an invalid email address, the corresponding error message should be displayed.Note: In the current scope of this blog, we are not working on styling.Is it possible to validate forms without built in APIs ? Let’s see with the same example.We would consider the same form again but have lot of functionality in                           Please enter an email address:                                             Submit           const form  = document.getElementsByTagName('form')[0];     const email = document.getElementById('mail');     let error = email.nextElementSibling;     const emailRegExp = /^[a-zA-Z0-9.!#$%&'*+/=?^_{|}~-]+@[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$/;     function addEvent(element, event, callback) {       let previousEventCallBack = element["on"+event];       element["on"+event] = function (e) {         const output = callback(e);         // A callback that returns false stops the callback chain and interrupts the execution of the event callback.         if (output === false) return false;         if (typeof previousEventCallBack === 'function') {           output = previousEventCallBack(e);           if(output === false) return false;         }       }     };     // Now we can rebuild our validation constraint. Because we do not rely on CSS pseudo-class, we have to explicitly set the valid/invalid class on our email field     addEvent(window, "load", function () {       // Here, we test if the field is empty (remember, the field is not required)       // If it is not, we check if its content is a well-formed e-mail address.       const test = email.value.length === 0 || emailRegExp.test(email.value);       email.className = test ? "valid" : "invalid";     });     // This defines what happens when the user types in the fiel     addEvent(email, "input", function () {       const test = email.value.length === 0 || emailRegExp.test(email.value);       if (test) {         email.className = "valid";         error.textContent = "";         error.className = "error";       } else {         email.className = "invalid";       }     });     // This defines what happens when the user tries to submit the data     addEvent(form, "submit", function () {       const test = email.value.length === 0 || emailRegExp.test(email.value);       if (!test) {         email.className = "invalid";         error.textContent = "Expecting an e-mail";         error.className = "error active";         return false;       } else {         email.className = "valid";         error.textContent = "";         error.className = "error";       }     });   On refreshing the page, the output with invalid email address should be displayed as shown below.In real time applications, we can rely on existing libraries like Parsley along with JQuery which would ease our life by taking away lot of complexity.Overview of Parsley:Parsley is a front-end javascript validation library which helps to give proper feedback to user on submission of form. As mentioned earlier, it is not a replacement of server side validation. Parsley library helps us to define our own validation.Parsley uses a DOM API namely ‘data-parsley-’ prefix on the existing properties. For example if we want to add this on a property say ‘sample’ then we would add as [data-parsley-sample=’value’]. This will allow us to configure pretty much everything without any configuration or custom function.There is no specific installation process but adding the corresponding script tags will enable the validation. Parsley is relied on Jquery so it has to be included as well.             ...                 $('#form').parsley(); Assumption is that we have downloaded the Jquery and Parsley minified librarie and added it to our working directory. Otherwise we can refer to CDN location as shown below. Adding attribute ‘data-parsley-validate’ to each form will allow us to validate. And “$(‘#form’).parsley()” will manually bind Parsley to your forms.Let’s understand further by configuring the attributes via JavaScript. For which, lets add two input fields inside the form element.                 Also let’s update the content to perform some pre-defined validation based on attributes.       var instance = $('#first').parsley(); console.log(instance.isValid()); // maxlength is 42, so field is valid$('#first').attr('data-parsley-maxlength', 4);       console.log(instance.isValid()); // No longer valid, as maxlength is 4       // You can access and override options in javascript too:       instance.options.maxlength++;       console.log(instance.isValid()); // Back to being valid, as maxlength is 5       // Alternatively, the options can be specified as:       var otherInstance = $('#second').parsley({ maxlength: 10 }); console.log(otherInstance.options); In the console.log, we should see thistrue false true {maxlength: 10}Options are inherited from the global level to form level and further to field. So if we set the options at global level then the same can be observed at field level. Parsley.options.maxlength = 42; // maxlength of 42 is declared at global level var formInstance =$('form').parsley(); var field = $('input').parsley(); console.log(field.options.maxlength); // Shows that maxlength is 42 inherited from global Parsley.options.maxlength = 30; console.log(field.options.maxlength); // Shows that maxlength is automatically 30 formInstance.options.maxlength++; console.log(field.options.maxlength); // Shows that maxlength is automatically 31We can also add our own custom validations. Let understand this with an example. window.Parsley.addValidator('multipleOf', { requirementType: 'integer', validateNumber: function(value, requirement) { return 0 === value % requirement; }, messages: { en: 'This value should be a multiple of %s', } }); Here we are adding a new attribute namely ‘data-parsley-multiple-of’ which takes only numeric values which are multiples of 3.In window.Parsley, we added a new validator with name ‘multiple-of’ with an object containing few important properties like ‘requirementType’, ‘validateNumber’ and ‘messages’ to be shown. This properties helps the library to check if the input value is valid or not.Similar to validateNumber, other properties are also there for different types like validateString, validateDate and validateMultiple.Also for requirementType, we have different options like string, number, date, regexp, boolean etc.Messages by default has English format, to support multiple locales we need to add the specific localization and also add specific locale.Events: Parsley triggers events that allows ParsleyUI to work and for performance reasons they don’t rely on JQuery events but the usage is similar to JQuery i.e. parsley events will also bubble up like JQuery events. For example, if a field is validated then the event ‘field:validate’ will be triggred on the field instance then on to form instance and finally to the window.Parsley.$('#some-input').parsley().on('field:success', function() {         // In here, this` is the parlsey instance of #some-input       });       window.Parsley.on('field:error', function() {         // This global callback will be called for any field that fails validation.         console.log('Validation failed for: ', this.$element); });Many times, we need some validation based on the response from server. Parsley provides an attributes i.e. data-parsley-remote and data-parsley-remote-validator to perform the same.Let’s consider this HTMLLet’s add the async validator on the window.Parsley object.window.Parsley.addAsyncValidator('customValidator', function (xhr) { console.log(this.$element); // jQuery Object[ input[name="q"] ]           return 404 === xhr.status;         }, 'customURL');Parsley is a very useful and powerful JavaScript form frontend validation library.Note: For developers building react based web applications, they can rely on FORMIK which is most popular library for building forms in React and React Native.ConclusionForms are important in HTML and it was needed and still needed now. is an html tag that allow us to perform HTTP methods like GET/POST operation without writing any code in JavaScript. Form defines an boundary to identify all set of the form field elements to be submitted to the server. For example, if we perform an enter key or clicking on submit button , the agent triggers form submission data based on each form field value to the server based on the action URL on the form.Before HTML5, all the elements are expected to be part of the to send the data to server. In HTML5, they maintained the backward compatibility and also enhanced the capabilities who may want to use AJAX and don’t want to rely on default behaviours i.e. they have enabled designers who expect more flexibility in having their form elements outside the form and still maintain the connections with the form.
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How to Work With Forms In JavaScript

Forms also referred as web forms are a very import... Read More