size of a function in memory

Question

I have been exploring the size of various objects in javascript using sizeof.js. When I examine the size of a function I get zero bytes no matter how many lines of code the function contains. For example:

alert(sizeof(
  function(){
    return 1;
  }
));

This returns a size of zero. Even if I give the function many lines of code I get a size of zero bytes. The amount of memory needed to store a string is dependent on the length of the string. But the complexity or size of a function seems to be irrelevant. Why is this so?

Arun P Johny · Accepted Answer · 2014-11-11 03:08:33Z

2

If you look at the source code of the sizeof library, you can find that the object type function is not handled in the sizeof library, so by default the size 0 is returned.

/*

sizeof.js

A function to calculate the approximate memory usage of objects

Created by Stephen Morley - http://code.stephenmorley.org/ - and released under
the terms of the CC0 1.0 Universal legal code:

http://creativecommons.org/publicdomain/zero/1.0/legalcode

*/

/* Returns the approximate memory usage, in bytes, of the specified object. The
 * parameter is:
 *
 * object - the object whose size should be determined
 */
function sizeof(object){

  // initialise the list of objects and size
  var objects = [object];
  var size    = 0;

  // loop over the objects
  for (var index = 0; index < objects.length; index ++){

    // determine the type of the object
    switch (typeof objects[index]){

      // the object is a boolean
      case 'boolean': size += 4; break;

      // the object is a number
      case 'number': size += 8; break;

      // the object is a string
      case 'string': size += 2 * objects[index].length; break;

      // the object is a generic object
      case 'object':

        // if the object is not an array, add the sizes of the keys
        if (Object.prototype.toString.call(objects[index]) != '[object Array]'){
          for (var key in objects[index]) size += 2 * key.length;
        }

        // loop over the keys
        for (var key in objects[index]){

          // determine whether the value has already been processed
          var processed = false;
          for (var search = 0; search < objects.length; search ++){
            if (objects[search] === objects[index][key]){
              processed = true;
              break;
            }
          }

          // queue the value to be processed if appropriate
          if (!processed) objects.push(objects[index][key]);

        }

    }

  }

  // return the calculated size
  return size;

}

You can see that size is initialized with value 0 and the type function is not handled in the switch statement so it will always return 0 for a function.

answered Nov 11, 2014 at 3:08

Arun P Johny

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3 Comments

gloo Over a year ago

I see. So does the memory needed at runtime to store a function indeed depend on the length of the function in terms of lines of code?

zerkms Over a year ago

@gloo: it depends on A LOT of things and may change in runtime if VM optimizer decides so.

Arun P Johny Over a year ago

@gloo I think the javascript interpreter makes some changes(optimization) so it will depends on lot of factors... also from what I have read the level of optimization might change based how often a function is used

zerkms · Accepted Answer · 2014-11-11 03:10:03Z

2

What sizeof.js does is just summarizes sizes of iterable attributes of an objects or plain sizes of scalar values. It uses the fixed known sizes of scalar values for that. So obviously the result is pretty much inaccurate.

It cannot calculate the size of a function because:

It is implementation dependent
It may even vary in runtime
ECMAScript does not declare how functions must be implemented

answered Nov 11, 2014 at 3:10

zerkms

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Comments

Wyzard · Accepted Answer · 2014-11-11 03:09:59Z

1

The website for sizeof.js says: "While JavaScript does not include a mechanism to find the exact memory usage of an object, sizeof.js provides a function that determines the approximate amount of memory used." (Emphasis mine.)

The result is "approximate" because it's limited by the information that the browser makes available, and the browser apparently doesn't provide size information for functions. This is unsurprising, since the code of a function — the actual bytecode or machine code that the browser executes — is an implementation detail that's not visible from within the program. A function is basically a black box.

answered Nov 11, 2014 at 3:09

Wyzard

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3 Comments

gloo Over a year ago

So is it reasonable to assume that a longer function will require more memory to store the function itself at runtime?

zerkms Over a year ago

@gloo: no, you better not make such assumptions

Wyzard Over a year ago

Functions that "do more" are likely to have a larger code size, but it's not directly related to the length of the function's source code.

Sean · Accepted Answer · 2014-11-11 03:15:34Z

0

it is too hard to determine how much memory a function is holding

all the local variable in that function need to be take into consideration, even clousure need to be take into count

as @Arun point out, function is not take into count in sizeof.js

answered Nov 11, 2014 at 3:15

Sean

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