You should
1. Use switch statement and literal character codes
or
2. Cache the reference character codes in closured variables
or
3. Obviously: Use a regular expression!
Good catch on the hash-miss thing - stored another
good-to-remeber-in-algorithm-choice snippet in my head.
On Wednesday, July 7, 2010 2:54:10 PM UTC+2, Chad wrote:
>
> I was surprised to find that a function call returning a boolean from
> a simple test was much (3x!) faster than an associative array
> lookup... I was wondering if someone could explain to me how that
> could be the case. Is v8 inlining the function somehow, or is the
> overhead of a function call extremely low?
>
> Note 1: I'm not complaining, I'm just curious as to how things were
> working under the covers.
> Note 2: The opposite is true for Firefox, which is 2x slower using the
> function call than the associative array... so an optimization for one
> would result in a performance regression for another... :(
>
> Example:
>
> ------
> isWhitespace:function(charCode) {
> return charCode == this.spaceCharCode || charCode ==
> this.tabCharCode || ... etc ...;
> },
>
> for (var i = 0; i < aString.length; i++) {
> var isWs = this.isWhitespace(aString.charCodeAt(i));
> }
> ------
>
> Is 3x faster than:
>
> ------
> whitespace: Associative array mapping whitespace char codes to true,
>
> for (var i = 0; i < aString.length; i++) {
> var isWs = this.whitespace[aString.charCodeAt(i)];
> }
> ------
>
> Thanks in advance, Chad
>
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