How to Check if Number is Integer in JavaScript

In JavaScript, you can check if a number is an integer using Number.isInteger(value), which returns true if the value is an integer and false otherwise. This method is the most reliable and modern way to perform this check.

Syntax

The syntax to check if a value is an integer is simple:

• Number.isInteger(value): Returns true if value is an integer, otherwise false.

Here, value is the number you want to test.

javascript

Number.isInteger(value)

Example

This example shows how to use Number.isInteger() to check different values:

javascript

console.log(Number.isInteger(25));      // true
console.log(Number.isInteger(25.0));    // true (25.0 is treated as 25)
console.log(Number.isInteger(25.5));    // false
console.log(Number.isInteger('25'));    // false (string, not number)
console.log(Number.isInteger(NaN));     // false
console.log(Number.isInteger(Infinity)); // false

Output

true
true
false
false
false
false

Common Pitfalls

Some common mistakes when checking for integers:

• Using typeof alone does not check if a number is integer.
• Comparing with parseInt can be misleading because it converts strings.
• Number.isInteger() only returns true for numbers of type number, not strings.

Here is a wrong and right way:

javascript

// Wrong way: using typeof only
const value = 25.5;
console.log(typeof value === 'number'); // true but value is not integer

// Right way: use Number.isInteger
console.log(Number.isInteger(value));   // false

Output

true
false

Quick Reference

Summary tips for checking integers in JavaScript:

• Use Number.isInteger(value) for a reliable check.
• Remember it returns false for non-number types.
• Do not rely on typeof or string conversions.

Key Takeaways

Use Number.isInteger(value) to check if a value is an integer in JavaScript.

Number.isInteger returns false for non-number types and decimal numbers.

Avoid using typeof or string parsing to check for integers.

Number.isInteger treats 25 and 25.0 as integers because they are the same number.