call prototype.call function in javascript

Question

the problem is that when i use test.call(), it calls into my call implementation of the prototype but when i use test(), it doesnt call call(). i want to be able to use test to trigger prototype.call(). code below:

            Function.prototype.call = function () {
            //do something...
            return this(); // call original method
        }

        function test() {
            alert("test");
        }

 test.call(); //calls prototype.call()
    test(); //doesnt call prototype.call()

cliffs of insanity · Accepted Answer · 2012-05-10 13:34:45Z

2

Why would you expect test() to invoke Function.prototype.call? They're different functions.

The native .call() method that you're overwriting is not invoked every time a function is invoked. It's only invoked when you invoke it.

Invoking .call() does invoke test() because that's what it's designed to do. It expects a function as its context (this value), and invokes that function. But that doesn't mean .call() has anything to do with any other function invocation.

answered May 10, 2012 at 13:34

cliffs of insanity

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12 Comments

Ali Tarhini Over a year ago

thanks for the clarification. So how is it possible to do it. I need to call a function whenever any other function is invoked.

ThiefMaster Over a year ago

It is simply not possible. Why do you think you need this?

cliffs of insanity Over a year ago

@AliTarhini: Not automatically. You could manually decorate the functions, but you'd need foreknowledge of those functions.

Ali Tarhini Over a year ago

I need to create a log of all functions being executed

ThiefMaster Over a year ago

Sounds like a job for a debugger.

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Elliot Bonneville · Accepted Answer · 2012-05-10 15:22:50Z

1

Here's a solution that I just whipped up (credit goes to cliffsofinsanity for pointing out a crucial error with the code and correcting it). It logs all non-standard functions called after a certain point, in the order that they were called.

// array of all called functions
var calledFunctions = [];

// custom func object that has name of function and 
// and the actual function on it.

function func(_func, name) {
    return function() {
        calledFunctions.push(name)
        return _func.apply(this, arguments);
    };
}

test = function() {
    alert("hi");
}

otherTest = function() {
    alert("hello");
}

// put this bit somewhere after you've defined all your functions
// but *before* you've called any of them as all functions called
// after this point are logged. It logs all non-standard functions
// in the order that they are called.
for (prop in window) {
    if (window.hasOwnProperty(prop) && typeof window[prop] === 'function' && window[prop].toString().indexOf('[native code]') < 0) {
        window[prop] = func(window[prop], prop);
    }
}

otherTest();
test();
otherTest();

console.log(calledFunctions);

Working demo can be found here.

edited May 10, 2012 at 15:22

answered May 10, 2012 at 14:27

Elliot Bonneville

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6 Comments

cliffs of insanity Over a year ago

Keep in mind that any arguments passed to the functions are lost, as well as the return value, and the context of the function may be altered. You should do return that._func.apply(this, arguments);. Also, you could really do this without a constructor. You're having to close over that to reference _func and name as properties, so instead you could skip the that object, and just close over the parameters. jsfiddle.net/TkZ6d/10

Elliot Bonneville Over a year ago

Very interesting, thanks for pointing that out! I've edited my answer and given you credit.

Ali Tarhini Over a year ago

just wondering what that means: window[prop].toString().indexOf('[native code]') < 0

Elliot Bonneville Over a year ago

@AliTarhini: It converts a property of the window to a string representation then checks to see if the string "[native code]" is found. If it is, then the property is something's "native" or standard to Javascript.

Ali Tarhini Over a year ago

thanks. The above code work perfectly. Is it possible to get script that is not embedded inside a function such as inline scripts that are writen directly inside script tags?

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