Null in JavaScript

Last Updated : 05 Jun, 2024

In JavaScript, `null` indicates the deliberate absence of any object value. It’s a primitive value that denotes the absence of a value or serves as a placeholder for an object that isn’t present. `null` differs from `undefined`, which signifies a variable that has been declared but hasn’t been assigned a value.

Syntax:

let number = null; console.log("Type of number is:" ,typeof number);

Null in JavaScript Example:

This example describes the Null value in JavaScript.

JavaScript

class Square {     constructor(length) {         this.length = length;     }     get area_of_square() {         return Math.pow(this.length, 2);     }      // Static function that returns the length     static create_function(length) {         return length > 0 ? new Square(length) : null;     } }  let variableOne = Square.create_function(10); console.log(variableOne.area_of_square);  let variableTwo = Square.create_function(); console.log(variableTwo); // null

Output:

100 null

Explanation:

Here, there is a Square class that has a constructor that takes length as the argument. The Square class has a static method named create_function() which returns a new Square object that has a specified length. Here, there are two scenarios one in which we pass an argument and another one in which we do not pass an argument.

In the first scenario, we create variableOne that creates a new object of Square, and a value of 10 is passed in the create_function() method. In the second scenario, we have created variableTwo but we do not pass anything there and therefore it returns a null as output.

Null in JavaScript Example:

Another example that will illustrate Null in JavaScript.

JavaScript

const var1 = null; if (var1) { console.log('var1 is not null'); } else { console.log('var1 is null'); }

Output:

var1 is null

Explanation:

Here, we have declared var1 as null. As we know that var1 is a falsy value therefore the else block gets executed only.

Use Cases of Null in JavaScript

1. Object Initialization:

If an object couldn’t be created, returning null is a common practice:

JavaScript

class Square {   constructor(length) {     this.length = length;   }   static createSquare(length) {     return length > 0 ? new Square(length) : null;   } }  const square1 = Square.createSquare(10); // Creates a valid Square object const square2 = Square.createSquare();   // return null  console.log(square1); console.log(square2);

Output:

Square { length: 10 } null

2. Checking for null:

Use null to indicate that a value is intentionally absent:

JavaScript

const myValue = null; if (myValue) {   console.log("Not null"); // This won't execute } else {   console.log("Null"); // Output: "Null" }

Output:

Null

Key Takeaways

null is a falsy value.
It represents the intentional absence of an object value.
Use it wisely in your code to convey specific meanings.

Remember, mastering null will enhance your JavaScript skills.

JavaScript uneval() Function

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