Get body of function in JavaScript

Question

i am trying to get the body of a function in JavaScript but am unable to do so. Let's say I wanted to see the function body of the native toUpperCase() function of the String object:

document.write(String.prototype.toUpperCase.toString()); 
// returns function toUpperCase() { [native code] }

I tried this in Safari, Chrome, Firefox, all return the same thing. How do I access what that [native code] contents is?

* update *

The reason I stumbled onto this question, is because I was trying to do the following:

If I have two functions, one of which I want to invoke on the other, I want to access the first function's return value in the second, so that I can do function1().function2(). For example:

// create a global function that returns a value
function returnValue() {
   x = "john";
   return x;
}

// create a function that converts that value to uppercase
   function makeUpperCase(){
   return this.toUpperCase(); 
   // "this" obviously doesn't work, but "this" is where I wanted to
   // access the return value of a function I'm invoking makeUpperCase() on.
}

So I wanted to see how a function like toUpperCase() accesses the return value of a function it is invoked on.

you can't - at least not with JavaScript... you would need to load the JavaScript-implementation (usually some DLL) into a disassembler... — Yahia
– Yahia, Commented Oct 26, 2011 at 19:02
In your example you can use makeUpperCase.apply(returnValue()). This will make the 'this' in makeUpperCase be the returned string, thus making it call the string's toUpperCase method — Tom Knapen
– Tom Knapen, Commented Oct 26, 2011 at 19:10
Doesn't sound like you really need the body. I think you should look into function chaining. — Mike Robinson
– Mike Robinson, Commented Oct 26, 2011 at 19:10

gen_Eric · Accepted Answer · 2011-10-26 19:22:11Z

1

You can add a function to String.prototype, then you can "chain" your function calls.

String.prototype.makeUpperCase = function(){
  // 'this' is the string that 'makeUpperCase' was called on
  return this.toUpperCase();
};

var y = returnValue().makeUpperCase();

Chaining works by having the functions be part of the object, String.prototype in this case. So, when you return that object (a string), you can call another function on it ("chaining").

edited Oct 26, 2011 at 19:22

answered Oct 26, 2011 at 19:14

gen_Eric

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