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In this article, we will look into query string module in Node.js, and understand a few methods to deal with query string. The available methods can be used to convert query string into a JSON object and convert a JSON object into query string.
A query string according to Wikipedia is a part of the uniform resource locator (URL), that assigns values to specified parameters. In plain English it is the string after the ? in a url. Some url examples are shown below.
https://example.com/over/there?name=ferret https://example.com/path/to/page?name=ferret&color=purple
The query string in first case is name=ferret and in second case is name=ferret&color=purple
Now, the Node.js query string module provides methods for parsing and formatting URL query strings. The query string module can be accessed using the below –
const querystring = require(‘querystring’)
We will now look into the below six methods in the next section.
Let us look into a real example to understand the important Query string methods. Let us setup a basic Node application by giving the command npm init -y in terminal, inside a folder. I had created an empty NodeJS folder for the same.
$ npm init -y
Wrote to D:\NodeJS\package.json:
{
"name": "NodeJS",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"keywords": [],
"author": "",
"license": "ISC"
}The above commands create a basic package.json file, which is the basis of any Node.js project. We are using the -y option, so that we don’t have to enter the details manually.
Next, open the folder in a code editor which is VSCode in my case. Here, I have created a file querystring.js and the first line contains the importing of querystring module.
querystring.parse() Method
The querystring.parse() method is used to parse the URL query string into an object that contains the key value pair. The object which we get is not a JavaScript object, so we cannot use Object methods like obj.toString, or obj.hasOwnProperty().
The latest UTF-8 encoding format is assumed unless we specify a different encoding format. But we should stick to UTF-8 encoding as it is the standard and contains all international characters like the Chinese characters and the hindi characters. After that also if we need alternative character encoding, then the decodeURIComponent option should be used.
The syntax for the method is below.
querystring.parse( str[, sep[, eq[, options]]]) )
As seen from the above syntax the method accepts four parameters, and they are described below.
The below example shows the various options used in querystring.parse() method. Add the below code in querystring.js file, which we created earlier.
.jpg&w=3840&q=75)
// Import the querystring module
const querystring = require("querystring");
// Specify the URL query string to be parsed
let urlQueryString = "name=nabendu&units=kgs&units=pounds&login=false";
// Use the parse() method on the string
let parsedObj = querystring.parse(urlQueryString);
console.log("Parsed Query 1:", parsedObj);
// Use the parse() method on the string with sep as `&&` and eq as `-`
urlQueryString = "name-nabendu&&units-kgs&&units-pounds&&login-true";
parsedObj = querystring.parse(urlQueryString, "&&", "-");
console.log("\nParsed Query 2:", parsedObj);
// Specify a new URL query string to be parsed
urlQueryString = "type=admin&articles=java&articles=javascript&articles=kotlin&access=true";
// Use the parse() method on the string with maxKeys set to 1
parsedObj = querystring.parse(urlQueryString, "&", "=", { maxKeys: 1 });
console.log("\nParsed Query 3:", parsedObj);
// Use the parse() method on the string with maxKeys set to 2
parsedObj = querystring.parse(urlQueryString, "&", "=", { maxKeys: 2 });
console.log("\nParsed Query 4:", parsedObj);
// Use the parse() method on the string with maxKeys set to 0 (no limits)
parsedObj = querystring.parse(urlQueryString, "&", "=", { maxKeys: 0 });
console.log("\nParsed Query 5:", parsedObj);Now, run the command node querystring.js from the Integrated terminal in VSCode or any terminal. Note that you need to be inside the folder NodeJS, which we had created earlier. The output of the same will be below.
Parsed Query 1: [Object: null prototype] { name: 'nabendu', units: [ 'kgs', 'pounds' ], login: 'false' }
Parsed Query 2: [Object: null prototype] { name: 'nabendu', units: [ 'kgs', 'pounds' ], login: 'true' }
Parsed Query 3: [Object: null prototype] { type: 'admin' }
Parsed Query 4: [Object: null prototype] { type: 'admin', articles: 'java' }
Parsed Query 5: [Object: null prototype] {
type: 'admin',
articles: [ 'java', 'javascript', 'kotlin' ],
access: 'true' }querystring.stringify() Method
The querystring.stringify() method is used to produce a query string from a given object, which contains a key value pair. It is exactly the opposite of querystring.parse() Method.
It can be used to convert the string, numbers and Boolean values for the key. You can also use an array of string, numbers or Boolean as values. This method of changing an object to query string is called serialized.
The latest UTF-8 encoding format is assumed unless we specify a different encoding format. But we should stick to UTF-8 encoding as it is the standard and contains all international characters like the Chinese characters and the Hindi characters. If we still need an alternative character encoding, then the decodeURIComponent option should be used.
Syntax for the method is below.
querystring. stringify( obj[, sep[, eq[, options]]]) )
As from the above syntax the method accepts four parameters, and they are described below.
The below example shows the various options used in querystring.stringify() method. Add the below code in querystring.js file, which we created earlier.
// Import the querystring module
const querystring = require("querystring");
// Specify the object that needed to be serialized
let obj = {
name: "nabendu",
access: true,
role: ["developer", "architect", "manager"],
};
// Use the stringify() method on the object
let queryString = querystring.stringify(obj);
console.log("Query String 1:", queryString);
obj = {
name: "Parag",
access: false,
role: ["editor", "HR"],
};
// Use the stringify() method on the object with sep as `, ` and eq as `:`
queryString = querystring.stringify(obj, ", ", ":");
console.log("Query String 2:", queryString);
// Use the stringify() method on the object with sep as `&&&` and eq as `==`
queryString = querystring.stringify(obj, "&&&", "==");
console.log("\nQuery String 3:", queryString);Now, run the command node querystring.js from the Integrated terminal in VSCode or any terminal. Note that you need to be inside the folder NodeJS, which we had created earlier. The output of the same will be below.
Query String 1: name=nabendu&access=true&role=developer&role=architect&role=manager
Query String 2: name:Parag, access:false, role:editor, role:HR
Query String 3: name==Parag&&&access==false&&&role==editor&&&role==HR
querystring.decode() Method
The querystring.decode() method is nothing but an alias for querystring.parse() method. In our parse example, we can use it. So, add the below code in querystring.js file, which we created earlier.
// Import the querystring module
const querystring = require("querystring");
// Specify the URL query string to be parsed
let urlQueryString = "name=nabendu&units=kgs&units=pounds&login=false";
// Use the parse() method on the string
let parsedObj = querystring.decode(urlQueryString);
console.log("Parsed Query 1:", parsedObj);As earlier, run the command node querystring.js from a terminal. And the output will be same as that with querystring.parse() method.
Parsed Query 1: [Object: null prototype] { name: 'nabendu', units: [ 'kgs', 'pounds' ], login: 'false' }querystring.encode() Method
The querystring.encode() method is nothing but an alias for querystring.stringify() method. In our stringify example, we can use it. So, add the below code in querystring.js file, which we created earlier.
// Import the querystring module
const querystring = require("querystring");
// Specify the object that needed to be serialized
let obj = {
name: "nabendu",
access: true,
role: ["developer", "architect", "manager"],
};
// Use the stringify() method on the object
let queryString = querystring.encode(obj);
console.log("Query String 1:", queryString);As earlier run the command node querystring.js from a terminal. And the output will be same as that with querystring.stringify() method.
Query String 1: name=nabendu&access=true&role=developer&role=architect&role=manager
querystring.escape(str) Method
The querystring.escape() method is used by querystring.stringify() method and is generally not used directly.
querystring.unescape(str) Method
The querystring.unescape() method is used by querystring.parse() method and is generally not used directly.
Summary
In this article we learnt about the useful query string module in Node.js, which is mainly used to parse URL query strings into Object format and also to change an object to URL query strings.
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