JS detects whether a function is a JavaScript native function

In my development work, I often encounter situations where it is necessary to determine whether a function is a JavaScript native function, and it is sometimes a necessity to know if the function is provided by the browser itself or by a third party, disguised as a native function. Of course, the best way to do this is to examine the return value of the ToString method that executes this function.

The JavaScript

The way to accomplish this task is simple:

The code is as follows	Copy Code
function Isnative (FN) { Return (/\{\s*\[native code\]\s*\}/). Test (' + FN '); }

The ToString method returns the string form of the method and then uses the regular expression to determine which characters are contained within it.

More powerful way.

Lodash's founder, John-david Dalton, found a better solution:

The code is as follows

Copy Code

;(function () { Used to resolve the internal ' [[Class]] ' of values var toString = Object.prototype.toString; Used to resolve the decompiled source of functions var fntostring = Function.prototype.toString; Used to detect host constructors (Safari > 4; really typed array specific) var rehostctor =/^\[object. +? constructor\]$/; Compile a regexp using a common native method as a template. We chose ' object#tostring ' because there ' a good chance it is not being mucked with. var renative = RegExp (' ^ ' + Coerce ' object#tostring ' to a string String (toString) Escape any special regexp characters . Replace (/[.*+?^${} () |[ \]\/\\]/g, ' \\$& ') Replace mentions of ' toString ' with '. ~ ' to keep the template generic. Replace thing like ' for ... ' to support environments like Rhino which add extra info such as Method arity. . Replace (/tostring| ( function). *? (? =\\\ () | for. +? (? =\\\]) /g, ' $1.*? ' + '$' ); function Isnative (value) { var type = typeof value; return type = = ' function ' Use ' function#tostring ' to bypass the value ' s own ' toString ' method And avoid being faked out. ? Renative.test (Fntostring.call (value)) Fallback to a host object check because some environments'll represent Things like typed arrays as DOM methods which may isn't conform to the Normal native pattern. : (value && type = = ' object ' && rehostctor.test (Tostring.call (value)) | | False } Export however you want Module.exports = isnative; }());

Now you see it, it's complicated, but it's more powerful. Of course, this is not for security protection, it just gives you information about whether it is a native function.