Detect if function is native to browser

Question

I am trying to iterate over all the globals defined in a website, but in doing so I am also getting the native browser functions.

var numf=0; var nump=0; v         


        

Answer 1

I tried a different approach. This is only tested for firefox, and chrome.

function isNative(obj){
    //Is there a function?
    //You may throw an exception instead if you want only functions to get in here.

    if(typeof obj === 'function'){
        //Check does this prototype appear as an object?
        //Most natives will not have a prototype of [object Object]
        //If not an [object Object] just skip to true.
        if(Object.prototype.toString.call(obj.prototype) === '[object Object]'){
            //Prototype was an object, but is the function Object?
            //If it's not Object it is not native.
            //This only fails if the Object function is assigned to prototype.constructor, or
            //Object function is assigned to the prototype, but
            //why you wanna do that?
            if(String(obj.prototype.constructor) !== String(Object.prototype.constructor)){
                return false;
            }
        }
    }
    return true;
}

function bla(){}

isNative(bla); //false
isNative(Number); //true
isNative(Object); //true
isNative(Function); //true
isNative(RegExp); //true