regex vs while loops

Question

While reading this SO post - Is there a version of JavaScript's String.indexOf() that allows for regular expressions?) I ponder which of the following two functions that

Answer 1

You can use jsPerf to compare the performance of different JavaScript snippets. I’ve created one that uses your two variants and this one by me:

function(str) {
    var parts = str.split(/(?=\s+)/);
    return parts.length === 1 ? -1 : str.length - parts[parts.length-1].length;
}

It basically splits the string at the position of the match using a look-ahead assertion. If no match is found, split returns an array with just one item; otherwise the length of the last part is subtracted from the total length of the string to get the index of the last match.

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Update    I’ve tweaked the functions a little bit and now we’ve got some completely different results compared to the previous benchmark. Now the first function that is now using /\s+(?!\S+\s+)/ instead of /\s+(?!.*\s+)/ seems to be the fastest.