For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt, and this page is available as Markdown at /reference/predicate/isNumber.md.
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    isNumber es-toolkit

    Checks if a value is a number type.

    const result = isNumber(value);

    Usage

    isNumber(value)

    Use isNumber when you want to check if a value is a number.

    import { isNumber } from 'es-toolkit';

// Checking basic number values
isNumber(123); // true
isNumber(3.14); // true
isNumber(NaN); // true
isNumber(Infinity); // true

// Distinguishing from other types
isNumber('123'); // false
isNumber(true); // false
isNumber(null); // false
isNumber(undefined); // false
isNumber(new Number(42)); // false

    Particularly useful when used as a type guard in TypeScript.

    import { isNumber } from 'es-toolkit';

function processValue(value: unknown) {
  if (isNumber(value)) {
    // value is narrowed to number
    console.log(value * 2);
  } else {
    console.log('Not a number');
  }
}

    Parameters

    valueunknownrequired

    The value to check if it's a number type.

    Returns

    Returns true if the value is a number, false otherwise.

    value is number
    Source: es-toolkit

    Re-exported verbatim from es-toolkit. Implementation, edge cases, and performance behavior are owned upstream. This page mirrors the documentation at the pinned version; the linked source is authoritative.