Two examples of JavaScript that determine native functions

Original link: Detect If a Function is Native Code with JavaScript
Original Date: 2014-08-17
Translation Date: 2014-08-20
Translators: Anchor

I always run into situations where I need to check if a function is native code-a very important part of the functional test: whether the function is built-in to the browser or simulated by a third-party class library. The simplest way to detect this is, of course, to judge the function toStringThe value returned by the method.

JavaScript code

Determining whether a function is a native method is actually quite simple:

Determine if the primary function isnative (FN) {    ////    alert.tostring ()//    "function alert () {[native code]}"    //' ' + FN takes advantage of the implicit type conversion of JS.    Return (/\{\s*\[native code\]\s*\}/). Test (' + fn);}

Converts a function to a string representation and performs a regular match, which is how the implementation works.

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Lodash's author John-david Dalton shared a better approach:

;(function () {//Gets the ToString method of Object that handles the internal (internal) ' [[Class]] ' var tostring = Object.prototype.toString of the incoming parameter value;    Gets the original Function of the ToString method, which is used to handle functions's anti-compile code var fntostring = Function.prototype.toString; Used to detect the Host object constructor (host constructors),//(Safari > 4; True output-specific array, really typed array specific) var rehostctor =/^\[obje Ct. +?  constructor\]$/;  Use regexp to compile common native methods into regular templates. Use ' object#tostring ' is because generally he will not be contaminated var renative = RegExp (' ^ ' +//Will ' object#tostring ' strong to String (toString)/ /escapes special characters related to all regular expressions. Replace (/[.*+?^${} () |[    \]\/\\]/g, ' \\$& ')//in order to maintain the versatility of the template, the ' toString ' is replaced with '. * '///replace ' for ... ' characters, compatible with environments such as rhino, as they will have additional information, such as the number of parameters for the method. . Replace (/tostring| ( function). *? (? =\\\ () | for. +? (?=\\\])    /g, ' $1.*? ')    Terminator + ' $ ');    function Isnative (value) {//judgment typeof var type = typeof value;      return type = = ' function '//use ' function#tostring ' native method to invoke,//rather than value own ' toString ' method,//To avoid being deceived by forgery. ? RenativE.test (Fntostring.call (value))//If type is not ' function ',//You need to check the host object's case,//because some (browser) environment will Typ Ed arrays things like DOM methods//This may not match the standard native regular mode: (value && type = = ' object ' && rehostctor.test (t Ostring.call (value))) | |  False    }; You can assign isnative to the variable/object you want window.isnative = isnative;} ());

Test Code:

Isnative (isnative)                  //falseisnative (Alert)                        //truewindow.isnative (window.isnative)//falsewindow.isnative (Window.alert)       Truewindow.isnative (string.tostring)    //true