# Xamarin Profiler and Memory Management

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App memory management has become one of the key priorities for any developer today. With new-gen energy-efficient processors launching every day &  operating systems shifting towards efficient power usage along with sleek UI experience, today’s developers face a challenge of developing apps that are sleek & efficient in memory management along with an intelligent tool to check memory leakage proactively. In this article, I will be covering two major topics i.e. xamarin profiler (Part 1) and memory management (Part 2).

## Part 1: Xamarin Profiler

### Introduction to Xamarin Profiler:

Xamarin Profiler is a tool developed by Microsoft that helps the developers to analyze the app's behavior, and its memory allocations with the help of a visual studio. It is a graphical interface that supports doing profiling in android, iostvos, mac applications in mac and android, iostvos applications in windows.

## Why use a profiler:

We all know that sometimes we don't properly dispose of the objects and therefore the garbage collector will not collect them and remove them from the memory.

In other words, with the help of the profiler, we can check memory leaks that are being held by objects which should ideally be disposed of.  Before that, let's understand how the operating system manages the memory.

There are two types of memory, native memory and managed memory. All the ios and android related objects like views, example buttons, text views fall into the native memory and the dot net-related objects, for example, subscriptions, event handlers, threads go into managed memory. Whenever there is a process, the operating system gives a small piece of this memory chunk to xamarin mono. So in order to check the memory allocations of managed memory, we need a profiler.

### Garbage Collector:

Before getting started with the profiler, let's understand what a garbage collector is. The garbage collector collects the disposed objects and frees up the memory.  As I discussed above there are two memory worlds in the operating system, native memory, and managed memory. Sometimes garbage collectors cannot do their job, because some of the dot net objects may be holding reference to native objects or vice versa. In such cases, it is difficult to understand where the memory leak is happening. So this is where the profiles come into the picture.

### Prerequisites:

Visual Studio (Mac or Windows)

Device or emulator

Step 2: Click on the Next button on the window Step 3: Click on the checkbox to agree to the license agreement and click next.

Step 4: Choose the destination folder where you want to install the xamarin profiler and click next again.

Step 5: Click on the install button and wait until the installation completes.

Now that we have successfully installed the profiler, we will have to launch it. But before that, we have to enable profiling in our app. Let's discuss that in the next section.

## Launching Profiler From Visual Studio:

Select android project, right-click and select properties,

Build ---> Android Debug---> Android options ---> Enable Developer Instrumentation

Once the above step is completed, open visual studio and load your application and keep the app in default debugging mode. Now go to Analyze---> Xamarin Profiler. Once you click on xamarin profiler, the profiler starts profiling automatically.

In case you don't see the xamarin profiler option, check the troubleshooting guide in the below link.

Deep Dive Into Profiler Instruments:

Xamarin profiler consists of three main instruments for profiling and they are allocations, cycles and time profiler. Let us understand how each of them works.

1. Allocations: Allocations chart is at the top of the profiler as shown in the below figure. Allocations represent the amount of memory being collected by the garbage collector at regular intervals of time during profiling. This instrument uses three data views that help the developer to understand how much of the memory is being used and released.

• Allocations: This represents the memory allocated by the classes and their associated methods. When you select a class, it shows the memory allocated to that particular class

• Call Tree: This displays the call tree of the threads used in the application. In other words, it shows the memory allocated to each thread.

• Snapshots: This section displays what memory is retained and released. To generate this information, you need to click on the camera button on the toolbar as shown in the below figure. The snapshots information can be captured only during live profiling.

2. Time Profiler: This instrument represents the amount of time taken by each method in the application. The application is paused at regular intervals and a stack trace is run on each thread.

3. Cycles: We often never dispose of the objects as sometimes they will be holding a reference to other objects. The cycles instrument represents the cycle of these objects in the application.

Part B:

Memory Management:

Introduction: When it comes to a mobile application or a website, it is always necessary to ensure proper management of objects and resources to avoid sluggishness when using the app. If not taken care of, it would lead to slow performance and crashes when used continuously. In this article, I will discuss how to prevent memory leaks and improve the performance of the app.

Common Memory Leaks: Memory leaks can be very dangerous because they lead to crashes if allocated memory is full. They can show down the app performance and sometimes make it unresponsive.

Let us see few of the common memory leaks that we make while developing our applications.

• Subscribing or registering to event handlers, delegates and messaging centers can cause memory leaks if not unsubscribed and unregistered at the right place.
• Using views, example buttons and images cause a memory leak because the garbage collector does not collect them until they are disposed of.
• Caching mechanisms to store data can cause out of memory exceptions because the memory keeps filling up and the app crashes.
• Threads should be used carefully because any reference objects will not be collected by the garbage collector.
• Using static variables, events are GC roots and are not collected by the garbage collector.
• Using bindings can cause memory leaks. So always bind to the dependency object or INotifyPropertyChanged to avoid memory leaks. Avoid using bindings in unnecessary places.

Steps for preventing memory leaks:

Below are a few approaches to avoid memory leaks. They not only improve the performance of the app, but also reduce the work done by the CPU. Let’s discuss them one by one.

1. Use of Asynchronous operations: We can use asynchronous operations to many of our functions especially for long-running tasks. Asynchronous operations do not block the UI thread and ensure a smooth transition of user interactions. To enable asynchronous operations, dot net provides async and await keywords which can be used to call asynchronous APIs.

2. Reducing the application size: In order to reduce the application size, we need to understand the compilation process of each platform.

Android uses a just-in-time (JIT) compiler to convert to an intermediate language.

Windows uses a built-in-time compiler to convert to an intermediate language.

Ios uses an ahead-of-time compiler to convert to ARM assembly language.

For all of these platforms, appropriate linker options should be selected in order to strip off the unused framework class. By default, in xamarin the linker is disabled. We need to enable the correct linker so that during the run time, the application determines which members, types are used and removes the unused types.

To understand how to select an appropriate linker, go through the below link

3. Optimizing image assets: Images are the most expensive resources an application can have as we use them at high resolutions and they occupy a lot of memory. We need to optimize images based on the phone resolution by having different resolutions and fit them based on the phone size. For example, use a small resolution image if you are using it in a listview rather than a big image that fits a full screen because there is a lot of CPU wastage to decode them to smaller sizes. Also, use the images only when required and release them when not in use.

4. Profilers: Profiler is a great tool to analyze the application behavior and check for memory leaks. They can also be combined with native instruments to check memory allocations of native objects. I hope you already know how to use them as we have discussed xamarin profilers in PART- A.

5. Test for memory leaks in the app: It is always best practice to test memory leaks for every function you do. Below is the sample code to test memory leaks.

[Test]
void MemoryLeakTest()
{
var weakReference = new WeakReference(leakyObject)
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();
Assert.IsFalse(weakReference.IsAlive);
}


6. Unsubscribe from events: It is always best practice to unsubscribe from events to dispose of them so that the garbage collector does its job. We often forget to do that and this leads to memory leaks as the object is still holding the reference and keeps it alive. This has to be taken care of whenever using threads, messaging center, event handlers, and delegates. Below is the sample code to unsubscribe from events and dispose of them

public class EventDemo
{
public event EventHandler DemoEvent;
public void OnMyEventFires()
{
if (DemoEvent != null)
{
DemoEvent(this, EventArgs.Empty);
}
}
}
public class SubscriberDemo : IDisposable
{
public SubscriberDemo(EventDemo  _eventDemo)
{
eventDemo = _eventDemo;
eventDemo.DemoEvent += OnDemoEventFires;
}
void OnDemoEventFires(object sender, EventArgs e)
{
Debug.WriteLine("The publisher notified the subscriber of an event");
}
public void Dispose()
{
eventDemo.DemoEvent -= OnDemoEventFires;
}
}

Using Dispose Pattern: The dispose method is used to release unmanaged resources. Our garbage collector does not allocate or release unmanaged memory. The pattern for releasing these objects is called a dispose pattern. In order to use the dispose method, you need to inherit your class with IDisposableInterface.  Below is the code snippet showing how to use dispose method.

 public void Dispose()
{
// Dispose of unmanaged resources.
Dispose(true);
// Suppress finalization.
GC.SuppressFinalize(this);
} 

Using Statement: Whenever working with files, steam readers, graphics in .Net framework, we create a lot of unmanaged code. By implementing the using statement, the code is transformed into a try/finally statement behind the scenes and the dispose method is called at the final clause. So ensure that you implement “using statement” whenever necessary.

public void CreateFile()
{
using (var stream = new FileStream(@"\Document\YourFile.txt",
FileMode.OpenOrCreate))
{

}// stream.Dispose()
} 

Size Reduction Techniques: Below are few approaches to reduce the application size.

• Always generate the build in release mode.
• Make sure the LLVM compiler is used.
• Enable the appropriate linker in each project (Link all for ios projects and Link all assemblies for android projects)
• Reduce the number of architectures to avoid FAT binary being produced.

Reducing Web Service Communication: We often make multiple calls over the web in order to transfer and receive data. This communication uses more network bandwidth and drains the phone's battery. As a result, there is a performance hit on our application. There are a few approaches that can help us here.

• The JSON format is always preferred as it uses lesser bandwidth while sending and receiving data over the network.
• Using data transfer objects (DTO) during data transfer between the mobile application and web service because more data can be transferred in a single remote call; thereby reducing the number of network calls.
• Once the web service call is made, it is preferred to cache the data locally instead of requesting the server multiple times.
• One more approach to reduce the network bandwidth is to compress data before transferring it over the network. However this might increase the CPU usage and drain the battery. Therefore this approach must be carefully evaluated before using it.

Conclusion:

To sum up the things we have covered, we now know what causes memory leaks, how to prevent them and how to use xamarin profiler to find memory allocations, improve application performance and do code optimization. So let us adapt to a routine to bring out these practices while building mobile applications.

I hope this article helps you and saves a lot of time. Please do share your feedback and let me know if you have any queries.

### Mounika Rajapuram

Mounika calls herself a dynamic professional with expertise in developing mobile applications for iOS and Android. With C# and Xamarin as primary areas of expertise, she also likes to dwell in doodle art in her pastime.

## 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