JavaScript Number isInteger() Method

What You’ll Learn

Number.isInteger() is a static method on Number (same API as MDN Number.isInteger). Call Number.isInteger(value) — not on a number instance. It returns true only for integer number values. This tutorial covers syntax, floats vs integers, precision quirks, five examples, and try-it labs.

Introduction

Counts, indexes, and page sizes are usually whole numbers. Number.isInteger() tells you whether a value is an integer — a number with no fractional part.

Like other static Number checks, it does not coerce strings: Number.isInteger("10") is false. Parse first when the input is text.

This page is part of JavaScript Number Methods. Related static checks include Number.isFinite() and Number.isNaN().

Understanding the isInteger() Method

Pass any value to Number.isInteger(value). You get true only when both of these are true:

• The type is "number".
• The number is an integer (including negatives and 0).

Infinity, -Infinity, NaN, floats like 0.1, and non-numbers all return false. Values written with .0 (such as 5.0) still count as integers.

📝 Syntax

General form of the static method Number.isInteger:

Number.isInteger(value)

Parameters

• value (any) — the value to test for being an integer.

Return value

A boolean:

Exceptions

• None for normal calls — invalid types simply return false.

Common patterns

Number.isInteger(0);          // true
Number.isInteger(-100000);    // true
Number.isInteger(0.1);        // false
Number.isInteger("10");       // false
Number.isInteger(5.0);        // true
Number.isInteger(10 / 5);     // true

Examples Gallery

Examples follow MDN patterns. Use View Output or Try It Yourself for each case.

Number.isInteger(0);  // true

true

Number.isInteger(-100000);  // true

true

Number.isInteger(0.1);  // false

false

Number.isInteger("10");  // false

false

Number.isInteger(10 / 5);  // true

true

🚀 Common Use Cases

• Indexes & counts — ensure page size, quantity, or array index is whole.
• Form validation — after parsing input, confirm an integer.
• Even division — Number.isInteger(y / x) for “fits evenly” checks.
• API contracts — reject fractional IDs or counts before saving.
• Game / grid logic — tile coordinates that must be integers.
• Pair with isFinite — first ensure finite, then optionally require integer.

📝 Notes

• This is a static method — use Number.isInteger(x) only.
• Does not coerce strings, booleans, arrays, or objects.
• Number.isInteger(5.0) is true — 5.0 is the same value as 5.
• Floating-point limits can surprise you near huge magnitudes (see MDN’s precision notes).
• Number.isInteger(5.000000000000001) is false, but an even tinier difference may round to 5 and return true.
• Integer is stricter than finite — use Number.isFinite() when decimals are allowed.

💡 Best Practices