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How to check if the provided value is of the specified type in JavaScript ?
  • Difficulty Level : Medium
  • Last Updated : 26 Mar, 2021

The following approach covers how to check if the provided value is of the specified type in JavaScript.

Approach: The Object.is() JavaScript method introduced in ECMAScript 2015 (popularly called ES6) determines whether two values are the same value. 

Object.is() determines whether two values are the same value. Two values are the same if both are undefined, both null, both true or both false, both strings of the same length with the same characters in the same order, both the same object (meaning both values reference the same object in memory), both numbers and both +0, both -0, both NaN, or both non-zero and both not NaN and both have the same value

Syntax : 

Object.is(value1, value2);

Parameters: This method accepts the following two parameters:



  • value1: It is the first value to compare.
  • value2: It is the second value to compare.

Return Value: This function returns the boolean value.

Example 1: 

index.js




// Evaluation result is the same as using ===
console.log(Object.is(25, 25));                // true
console.log(Object.is('foo', 'foo'));          // true
console.log(Object.is('foo', 'bar'));          // false
console.log(Object.is(null, null));            // true
console.log(Object.is(undefined, undefined));  // true
console.log(Object.is([], []));                // false
  
var foo = { a: 1 };
var bar = { a: 1 };
  
console.log(Object.is(foo, foo));              // true
console.log(Object.is(foo, bar));              // false

Run the index.js file using the following command:

node index.js

Output:

true
true
false
true
true
false
true
false

Example 2: 

index.js




// Signed Zero
console.log(Object.is(0, -0));                 // false
console.log(Object.is(+0, -0));                // false
console.log(Object.is(-0, -0));                // true
console.log(Object.is(0n, -0n));               // true
  
// NAN case
console.log(Object.is(NaN, 0/0));              // true
console.log(Object.is(NaN, Number.NaN))        // true

Run the index.js file using the following command:

node index.js

Output:

false
false
true
true
true
true

Key Difference Between Object.is() and === (Strict Equality)

  • Object.is(+0,0) is false, Object.is(NaN,NaN) is true.
  • So Object.is() is just === with different behavior for negative zero -0 and NaN.

Note: As an ES6 feature, it may not be supported by older browsers, but it can be transpired using Babel for compatibility.

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