Comments on: Easily cache results from Javascript functions

By: Gunnar Steinn

Gunnar Steinn — Wed, 23 Sep 2009 22:48:27 +0000

@jetm Thanks, fixed the link

By: jetm

jetm — Wed, 23 Sep 2009 17:54:30 +0000

URL:
http://www.gunnarsteinn.com/2009/09/easily-cache-results-from-javascript-functions/wp-content/cache.html

Is don’t working

By: Gunnar Steinn

Gunnar Steinn — Mon, 21 Sep 2009 17:03:09 +0000

Adrians approach works well except that arguments isn’t a proper Array in Javascript so you will have to use the “Array.slice.call(arguments).join(’|')” line from my code.

By: Bob

Bob — Mon, 21 Sep 2009 16:44:19 +0000

I came up with an alternative version as well, looks like Adrian beat me to it.

My commentary is here:

http://www.reddit.com/r/programming/comments/9mm5o/easily_cache_results_from_javascript_functions/c0deuu8

I put Adrian’s thing in there, to get the formatting back. Woo!

By: Adrian Quark

Adrian Quark — Mon, 21 Sep 2009 15:46:17 +0000

Sorry about the formatting, the blog software seems to lose indentation even though I used a block.


[EDIT: Fixed   Gunnar Steinn]



By: Adrian Quark
Adrian Quark — Mon, 21 Sep 2009 15:45:15 +0000
A few problems with this:

1. the .name property is a much easier way to get the name of a function.

2. this won’t work with anonymous functions.

3. because it uses a global cache the cached values won’t be garbage collected even if the function goes away (e.g. it’s an event handler).

4. if your function takes a variable number of arguments and one contains a “|” the cache won’t work correctly.

5. if the function returns null this won’t be cached

6. the cache key won’t work with Object values since they don’t have a unique string representation. You need to use something like http://www.timdown.co.uk/jshashtable/ to get around that.
You can fix 1-5 with some minor modifications:
function memoise(f) {
  var cache = {};
  return function () {
    var key = arguments.length+"|"+arguments.join("|");
    if (cache[key] === undefined) {
      cache[key] = f.apply(this, arguments);
    }
    return cache[key];
  }
}

isPrime = memoise(isPrime);