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/isBoolean.md.
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    isBoolean es-toolkit

    Checks if a value is a boolean type.

    const result = isBoolean(value);

    Usage

    isBoolean(value)

    Use isBoolean when you want to check if a value is exactly true or false. It acts as a type guard in TypeScript, narrowing the value's type to boolean.

    import { isBoolean } from 'es-toolkit/predicate';

// Checking basic boolean values
isBoolean(true); // true
isBoolean(false); // true

// Distinguishing from other types
isBoolean(1); // false
isBoolean(0); // false
isBoolean('true'); // false
isBoolean('false'); // false

    Particularly useful when used as a type guard in TypeScript.

    import { isBoolean } from 'es-toolkit/predicate';

function processValue(value: unknown) {
  if (isBoolean(value)) {
    // value is narrowed to boolean
    console.log(value ? "It's true" : "It's false");
  } else {
    console.log('Not a boolean value');
  }
}

    Can also be used for validating API responses or user input.

    import { isBoolean } from 'es-toolkit/predicate';

// Validating API response
interface APIResponse {
  success: unknown;
  data: any;
}

function validateResponse(response: APIResponse) {
  if (isBoolean(response.success)) {
    console.log(`API call ${response.success ? 'succeeded' : 'failed'}`);
    return response.success;
  }
  console.log('Invalid response format');
  return false;
}

    Parameters

    valueunknownrequired

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

    Returns

    Returns true if the value is true or false, false otherwise.

    value is boolean
    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.