JavaScript Number isSafeInteger() Method

What You’ll Learn

Number.isSafeInteger() is a static method on Number (same API as MDN Number.isSafeInteger). Call Number.isSafeInteger(value) — not on a number instance. It returns true only for integers inside the safe range. This tutorial covers syntax, MAX_SAFE_INTEGER, the difference from isInteger, five examples, and try-it labs.

Introduction

JavaScript numbers use IEEE-754 floating-point. Beyond about 15–16 significant digits, not every integer can be stored exactly — so IDs, counters, and money-in-cents math can silently lose precision.

Number.isSafeInteger() answers: “Is this an integer I can trust at full precision?” The safe range is Number.MIN_SAFE_INTEGER … Number.MAX_SAFE_INTEGER (±9,007,199,254,740,991).

This page is part of JavaScript Number Methods. Related checks include Number.isInteger(), Number.isFinite(), and Number.isNaN(). For larger exact integers, use BigInt.

Understanding the isSafeInteger() Method

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

• The type is "number".
• The value is an integer (same idea as Number.isInteger).
• It lies between Number.MIN_SAFE_INTEGER and Number.MAX_SAFE_INTEGER (inclusive).

Floats, strings, NaN, Infinity, and integers outside that range all return false.

📝 Syntax

General form of the static method Number.isSafeInteger:

Number.isSafeInteger(testValue)

Parameters

• testValue (any) — the value to test for being a safe integer.

Return value

A boolean:

Exceptions

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

Common patterns

Number.isSafeInteger(3);              // true
Number.isSafeInteger(2 ** 53 - 1);    // true
Number.isSafeInteger(2 ** 53);        // false
Number.isSafeInteger(3.1);            // false
Number.isSafeInteger("3");            // false
Number.isSafeInteger(Number.MAX_SAFE_INTEGER); // true

Examples Gallery

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

Number.isSafeInteger(3);  // true

true

Number.isSafeInteger(2 ** 53 - 1);  // true

true

Number.isSafeInteger(2 ** 53);  // false

false

Number.isSafeInteger(3.1);  // false

false

Number.isSafeInteger("3");  // false

false

🚀 Common Use Cases

• Database / API IDs — confirm IDs stay within precise Number range (or switch to BigInt/string).
• Counters & indexes — guard large tallies before increment math.
• Money in cents — keep integer amounts inside the safe range.
• Warn on precision loss — MDN-style helpers that flag unsafe magnitudes.
• Stricter than isInteger — when “whole number” is not enough.
• Choose BigInt — when values may exceed ±(2⁵³−1).

📝 Notes

• This is a static method — use Number.isSafeInteger(x) only.
• Does not coerce strings, objects, or booleans.
• Safe range: Number.MIN_SAFE_INTEGER … Number.MAX_SAFE_INTEGER.
• 2 ** 53 can look like an integer but is not safe — neighboring integers collide in floating-point.
• Every safe integer is an integer; not every integer is safe.
• For exact integers beyond the safe range, use BigInt.

💡 Best Practices