lodash/lang/isFunction.js

import isNative from './isNative';
import root from '../internal/root';

/** `Object#toString` result references. */
var funcTag = '[object Function]';

/** Used for native method references. */
var objectProto = Object.prototype;

/**
 * Used to resolve the `toStringTag` of values.
 * See the [ES spec](https://people.mozilla.org/~jorendorff/es6-draft.html#sec-object.prototype.tostring)
 * for more details.
 */
var objToString = objectProto.toString;

/** Native method references. */
var Uint8Array = isNative(Uint8Array = root.Uint8Array) && Uint8Array;

/**
 * Checks if `value` is classified as a `Function` object.
 *
 * @static
 * @memberOf _
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is correctly classified, else `false`.
 * @example
 *
 * _.isFunction(_);
 * // => true
 *
 * _.isFunction(/abc/);
 * // => false
 */
function isFunction(value) {
  // Avoid a Chakra JIT bug in compatibility modes of IE 11.
  // See https://github.com/jashkenas/underscore/issues/1621 for more details.
  return typeof value == 'function' || false;
}
// Fallback for environments that return incorrect `typeof` operator results.
if (isFunction(/x/) || (Uint8Array && !isFunction(Uint8Array))) {
  isFunction = function(value) {
    // The use of `Object#toString` avoids issues with the `typeof` operator
    // in older versions of Chrome and Safari which return 'function' for regexes
    // and Safari 8 equivalents which return 'object' for typed array constructors.
    return objToString.call(value) == funcTag;
  };
}

export default isFunction;