is-callable/index.js

'use strict';

var fnToStr = Function.prototype.toString;
var reflectApply = typeof Reflect === 'object' && Reflect !== null && Reflect.apply;
var badArrayLike;
var isCallableMarker;
if (typeof reflectApply === 'function' && typeof Object.defineProperty === 'function') {
	try {
		badArrayLike = Object.defineProperty({}, 'length', {
			get: function () {
				throw isCallableMarker;
			}
		});
		isCallableMarker = {};
		// eslint-disable-next-line no-throw-literal
		reflectApply(function () { throw 42; }, null, badArrayLike);
	} catch (_) {
		if (_ !== isCallableMarker) {
			reflectApply = null;
		}
	}
} else {
	reflectApply = null;
}

var constructorRegex = /^\s*class\b/;
var isES6ClassFn = function isES6ClassFunction(value) {
	try {
		var fnStr = fnToStr.call(value);
		return constructorRegex.test(fnStr);
	} catch (e) {
		return false; // not a function
	}
};

var tryFunctionObject = function tryFunctionToStr(value) {
	try {
		if (isES6ClassFn(value)) { return false; }
		fnToStr.call(value);
		return true;
	} catch (e) {
		return false;
	}
};
var toStr = Object.prototype.toString;
var fnClass = '[object Function]';
var genClass = '[object GeneratorFunction]';
var hasToStringTag = typeof Symbol === 'function' && !!Symbol.toStringTag; // better: use `has-tostringtag`
/* globals document: false */
var documentDotAll = typeof document === 'object' && typeof document.all === 'undefined' && document.all !== undefined ? document.all : {};

module.exports = reflectApply
	? function isCallable(value) {
		if (value === documentDotAll) { return true; }
		if (!value) { return false; }
		if (typeof value !== 'function' && typeof value !== 'object') { return false; }
		if (typeof value === 'function' && !value.prototype) { return true; }
		try {
			reflectApply(value, null, badArrayLike);
		} catch (e) {
			if (e !== isCallableMarker) { return false; }
		}
		return !isES6ClassFn(value);
	}
	: function isCallable(value) {
		if (value === documentDotAll) { return true; }
		if (!value) { return false; }
		if (typeof value !== 'function' && typeof value !== 'object') { return false; }
		if (typeof value === 'function' && !value.prototype) { return true; }
		if (hasToStringTag) { return tryFunctionObject(value); }
		if (isES6ClassFn(value)) { return false; }
		var strClass = toStr.call(value);
		return strClass === fnClass || strClass === genClass;
	};