Input validation
Validate numeric input before performing operations that require whole-number values.
JavaScript · Function
Number.isInteger
Number.isInteger() tests whether a value is a Number representing an integer. It does not coerce non-number values and returns false for NaN and infinities.
How it works
Call Number.isInteger(value) to test whether value is a Number representing an integer. It returns true for integral numeric values, including values such as 5.0, and false for non-numbers, non-integral numbers, NaN, and infinities; due to floating-point precision, some imprecise large values can still be classified as integers.
Syntax
Number.isInteger(value)Parameters
| Name | Type | Description |
|---|---|---|
value | any | The value to be tested for being an integer. |
Returns
A boolean: true if the given value is an integer; otherwise false.
Key points
- Number.isInteger is a static Number method for classifying a supplied value as an integer or not.
- Its call accepts one value argument.
- The value parameter is the item whose integer status is checked.
- The result is true when the value is an integer.
- A Number such as 5.0 passes because its represented numeric value is integral.
Common mistakes
- Numeric-looking strings, booleans, arrays, and other non-number values are rejected rather than converted.
- NaN and positive or negative infinity are never accepted.
- Floating-point representation can make a literal that appears fractional behave as an integer.
- Do not use this test alone when exact representation of large integers matters; consider Number.isSafeInteger().
Example: Testing integer values
const values = [5, 5.1, "5", NaN, 2 ** 53];
for (const value of values) {
console.log(value, Number.isInteger(value));
}Checks numbers without coercing strings or other non-number values.
When to use it
Runtime contracts
Reject fractional, string, boolean, NaN, or infinite values in API parameters.
Conversion guards
Check whether a value can be treated as an integer before converting it to BigInt.
Related
Number.isSafeInteger()Number.isFinite()Number.isNaN()Number.MAX_SAFE_INTEGER