JavaScript: Explain about void operator

void operator evaluates an expression and return undefined.

Syntax

void expression

void (expression)

Since ‘void expression’ return undefined, you can use this while checking for undefined variables.

HelloWorld.js

var x;
var y = 10;

if(x === (void 0)){
  console.log("x is undefined");
}else{
  console.log("Value of x is : " +  x);
}

if(y === (void 0)){
  console.log("y is undefined");
}else{
  console.log("Value of y is : " + y);
}

Output

x is undefined

Value of y is : 10

Example 1: Create hyper link that does nothing when user clicks on it

<a href="javascript:void(0)">Click here to do nothing</a>

When the user clicks on hyper link, void(0) returns undefined, which has no effect in JavaScript.

Example 2: Submit the form when user clicks on hyper link

<a href="javascript:void(document.form.submit())">Submit the form</a>

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