I’ve been doing some Javascript work lately where I’m doing a fair amount of string concatenation to build up some HTML, and I was curious to see whether the following syntax made any difference in performance:


string = string + "foo"


… vs:


string += "foo"


So I wrote up a little Javascript function to test this:


function startTrial() {
var resultDiv = document.getElementById("trialResults");
var myString = "";
alert("starting long method test");
var start = new Date();
for (var i=0;i<1000000;i++) { myString = myString + "a"; } var end = new Date(); var longMethodTime = end - start; myString = ""; alert("starting short method test"); start = new Date(); for (var i=0;i<1000000;i++) { myString += "a"; } end = new Date(); var shortMethodTime = end - start; var timeDiff = longMethodTime - shortMethodTime; var pctFaster = (timeDiff/longMethodTime) * 100; resultDiv.innerHTML = "Long Method = " + longMethodTime + "; Short Method = " + shortMethodTime + " (" + pctFaster + "% faster)"; }

The results (in ms) were a bit surprising:

IE 6 SP 2 (PC):

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Firefox 2 (Mac)

Firefox 3 (Mac)

Safari 3 (Mac)

Google Chrome:

These tests were all run on a Mac Pro - the IE and Chrome stats were done using Windows XP running on VMWare Fusion. Note that the performance is consistently better in IE6, but didn't really make a difference in any other browser.

If you're game, please try this for yourself; let me know how it goes for you!