PHP's is_callable in JavaScript

module.exports = functionis_callable (mixedVar, syntaxOnly, callableName) { // eslint-disable-line camelcase
//  discuss at: https://locutus.io/php/is_callable/
// original by: Brett Zamir (https://brett-zamir.me)
//    input by: François
// improved by: Brett Zamir (https://brett-zamir.me)
// improved by: KnightYoshi
// improved by: Waldo Malqui Silva (https://fayr.us/waldo/)
//      note 1: The variable callableName cannot work as a string variable passed by
//      note 1: reference as in PHP (since JavaScript does not support passing
//      note 1: strings by reference), but instead will take the name of
//      note 1: a global variable and set that instead.
//      note 1: When used on an object, depends on a constructor property
//      note 1: being kept on the object prototype
//      note 2: Depending on the `callableName` that is passed, this function can use eval.
//      note 2: The eval input is however checked to only allow valid function names,
//      note 2: So it should not be unsafer than uses without eval (seeing as you can)
//      note 2: already pass any function to be executed here.
//   example 1: is_callable('is_callable')
//   returns 1: true
//   example 2: is_callable('bogusFunction', true)
//   returns 2: true // gives true because does not do strict checking
//   example 3: function SomeClass () {}
//   example 3: SomeClass.prototype.someMethod = function (){}
//   example 3: var testObj = new SomeClass()
//   example 3: is_callable([testObj, 'someMethod'], true, 'myVar')
//   example 3: var $result = myVar
//   returns 3: 'SomeClass::someMethod'
//   example 4: is_callable(function () {})
//   returns 4: true
//   example 5: is_callable(class MyClass {})
//   returns 5: false
const $global = (typeofwindow !== 'undefined' ? window : global)
const validJSFunctionNamePattern = /^[_$a-zA-Z\xA0-\uFFFF][_$a-zA-Z0-9\xA0-\uFFFF]*$/
let name = ''
let obj = {}
let method = ''
let validFunctionName = false
const getFuncName = function (fn) {
const name = (/\W*function\s+([\w$]+)\s*\(/).exec(fn)
if (!name) {
return'(Anonymous)'
    }
return name[1]
  }
// eslint-disable-next-line no-useless-escape
if (/(^class|\(this\,)/.test(mixedVar.toString())) {
returnfalse
  }
if (typeof mixedVar === 'string') {
    obj = $global
    method = mixedVar
    name = mixedVar
    validFunctionName = !!name.match(validJSFunctionNamePattern)
  } elseif (typeof mixedVar === 'function') {
returntrue
  } elseif (Object.prototype.toString.call(mixedVar) === '[object Array]' &&
    mixedVar.length === 2 &&
typeof mixedVar[0] === 'object' &&
typeof mixedVar[1] === 'string') {
    obj = mixedVar[0]
    method = mixedVar[1]
    name = (obj.constructor && getFuncName(obj.constructor)) + '::' + method
  }
if (syntaxOnly || typeof obj[method] === 'function') {
if (callableName) {
      $global[callableName] = name
    }
returntrue
  }
// validFunctionName avoids exploits
if (validFunctionName && typeofeval(method) === 'function') { // eslint-disable-line no-eval
if (callableName) {
      $global[callableName] = name
    }
returntrue
  }
returnfalse
}