# Number.isSafeInteger()

The `Number.isSafeInteger()` method determines whether the provided value is a number that is a safe integer. A safe integer is an integer that

• can be exactly represented as an IEEE-754 double precision number, and
• whose IEEE-754 representation cannot be the result of rounding any other integer to fit the IEEE-754 representation.

For example, `253 - 1` is a safe integer: it can be exactly represented, and no other integer rounds to it under any IEEE-754 rounding mode. In contrast, `253` is not a safe integer: it can be exactly represented in IEEE-754, but the integer `253 + 1` can't be directly represented in IEEE-754 but instead rounds to `253` under round-to-nearest and round-to-zero rounding.

The safe integers consist of all integers from `-(253 - 1)` inclusive to `253 - 1` inclusive.

## Syntax

````Number.isSafeInteger(testValue)`
```

### Parameters

`testValue`
The value to be tested for being a safe integer.

### Return value

A `Boolean` indicating whether or not the given value is a number that is a safe integer.

## Examples

```Number.isSafeInteger(3);                    // true
Number.isSafeInteger(Math.pow(2, 53));      // false
Number.isSafeInteger(Math.pow(2, 53) - 1);  // true
Number.isSafeInteger(NaN);                  // false
Number.isSafeInteger(Infinity);             // false
Number.isSafeInteger('3');                  // false
Number.isSafeInteger(3.1);                  // false
Number.isSafeInteger(3.0);                  // true
```

## Polyfill

```Number.isSafeInteger = Number.isSafeInteger || function (value) {
return Number.isInteger(value) && Math.abs(value) <= Number.MAX_SAFE_INTEGER;
};
```

## Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Number.isSafeInteger' in that specification.
Standard Initial definition.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'Number.isSafeInteger' in that specification.
Draft

## Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) 32 (32) No support (Yes) No support
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support No support 32.0 (32) No support No support No support