is-arguments/index.js

Is this an arguments object? It's a harder question than you think.

'use strict';

var hasToStringTag = require('has-tostringtag/shams')();
var callBound = require('call-bound');

var $toString = callBound('Object.prototype.toString');

/** @type {import('.')} */
var isStandardArguments = function isArguments(value) {
	if (
		hasToStringTag
		&& value
		&& typeof value === 'object'
		&& Symbol.toStringTag in value
	) {
		return false;
	}
	return $toString(value) === '[object Arguments]';
};

/** @type {import('.')} */
var isLegacyArguments = function isArguments(value) {
	if (isStandardArguments(value)) {
		return true;
	}
	return value !== null
		&& typeof value === 'object'
		&& 'length' in value
		&& typeof value.length === 'number'
		&& value.length >= 0
		&& $toString(value) !== '[object Array]'
		&& 'callee' in value
		&& $toString(value.callee) === '[object Function]';
};

var supportsStandardArguments = (function () {
	return isStandardArguments(arguments);
}());

// @ts-expect-error TODO make this not error
isStandardArguments.isLegacyArguments = isLegacyArguments; // for tests

/** @type {import('.')} */
module.exports = supportsStandardArguments ? isStandardArguments : isLegacyArguments;