Number.isInteger() – JavaScript

In JavaScript, Number.isInteger() method checks whether the passed value is an integer or not. The method isInteger() returns true if the provided value is an integer or type number. Otherwise, it returns false.

Syntax

Number.isInteger(value)

Parameters:

value – The isInteger() method accepts a single parameter value that needs to be tested, and its a required parameter 

Return Value – The method Number.isInteger() returns a boolean value, i.e,. returns true if the target value passed is an integer. Otherwise, it returns false. If the value is NaN or Infinity, it returns false.

The isInteger() method returns true if you pass floating-point numbers that can be represented as an integer.

Let’s take few examples that illustrate the Number.isInteger() method in JavaScript.

Passing positive number as an argument 

 If you pass a positive value to the function as an argument, then it returns true. If the value passed is not of integer type, then it returns false.

console.log(Number.isInteger(77))

Output

true

Passing negative number as an argument 

 If you pass a negative value to the function as an argument, then it returns true. If the value passed is not of integer type, then it returns false.

console.log(Number.isInteger(-77))
console.log(Number.isInteger(-1.3))

Output

true
false

Passing zero as an argument 

 If you pass zero as an argument to the Number.isInteger() method, it returns true as 0 is an valid integer.

console.log(Number.isInteger(0))

Output

true

Passing floating-point number as an argument 

 If you pass a floating or decimal value to the function as an argument, it returns false as it’s not a valid integer.

console.log(Number.isInteger(34.33))
console.log(Number.isInteger(-1.4))

Output

flase
false

Passing floating-point number as an argument representing integer format

 If you pass a floating or decimal value representing an integer, the isInteger() method returns true as it can parse as a valid integer.

console.log(Number.isInteger(5.0)) //positive float representing as integer
console.log(Number.isInteger(5.0000000)) //positive float representing as integer
console.log(Number.isInteger(-12.0000000)) //negative float representing as integer
console.log(Number.isInteger(-5.000000000000001)) //negative float point number
console.log(Number.isInteger(-5.0000000000000001)) //negative float point number
console.log(Number.isInteger(-1.4))

Output

true
true
true
false
true
false

Passing string as an argument 

 If you pass a string as an argument to the Number.isInteger() method, it will return false. Even if you pass integer in string format, the method will return false as it cannot parse the string value.

console.log(Number.isInteger('hello'))
console.log(Number.isInteger('55'))

Output

false
false

Passing NaN, Infinity, Boolean as an argument 

 If you pass a NaN, Infinity, Boolean as an argument to the Number.isInteger() method, it will return false.

console.log(Number.isInteger(NaN))
console.log(Number.isInteger(Infinity))
console.log(Number.isInteger(-Infinity))
console.log(Number.isInteger(true))
console.log(Number.isInteger(false))

Output

false
false
false
false
false

Polyfill for Number.isInteger()

If you are looking for a Polyfill, you could use the code below if your browser is not supported.

Number.isInteger = Number.isInteger || function(value) {
  return typeof value === 'number' &&
    isFinite(value) &&
    Math.floor(value) === value;
};

Supported Browsers:

• Google Chrome: 34
• Edge: 12
• Internet Explorer: Not Supported
• Firefox: 16
• Apple Safari: 09
• Opera: 21