Comments on: A simple map function for plain JavaScript arrays

By: thomd

thomd — Sun, 05 Dec 2010 23:14:28 +0000

what about:

Array.prototype.map = function(fn) {
for (i = this.length; this[i] = fn(this[i--]); );
return this;
};

By: jesus

jesus — Wed, 03 Nov 2010 13:56:35 +0000

it would be best if you did r = new Array(l)

By: argimenes

argimenes — Sun, 05 Sep 2010 23:29:49 +0000

Nice article… with respect to concise syntax, you could try:

Array.prototype.map = function(fn) {
for (i=0, r=[], l = this.length; i < l; r.push(fn(this[i++])));
return r;
};

By: A simple map function for plain JavaScript arrays | Lazycoder

A simple map function for plain JavaScript arrays | Lazycoder — Thu, 13 Aug 2009 19:39:43 +0000

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JavaScript: Not for the faint at heart? | Lazycoder — Thu, 13 Aug 2009 16:22:39 +0000

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By: Scott

Scott — Thu, 13 Aug 2009 03:23:29 +0000

Duncan: with a for-in loop and a JavaScript array, you end up looping over all members of the Array type. If you have modified the prototype of the native Array, you’ll end up iterating over them as well. See this post for a better explanation as well as a way to avoid that.

http://www.lazycoder.com/weblog/2008/05/23/modern-javascript-development-reflection-in-javascrpt/

edit: Ok, that post I linked to helps if you are dealing with objects that are not native JavaScript objects. Native JavaScript objects are a little bit different. The members of native JavaScript objects are marked as non-enumerable, so for-in works on them provided that their prototype object has not been modified. If it has, you’ll have to use a combination of the technique described in the post aboce as well as special casing out the members you know have been added to the native JavaScript object.

By: Nate Kohari

Nate Kohari — Wed, 12 Aug 2009 23:44:36 +0000

Very useful. (I have a similar implementation myself.) By the way, I’ve used this sort of syntax for loops:

for (int idx = 0, len = arr.length; idx++; idx < len) {
…
}

By: Duncan Smart

Duncan Smart — Wed, 12 Aug 2009 21:35:48 +0000

What about sparse arrays? (ok, maybe they’re rare on the wild) How about for … in to loop through?