Javascript string performance comparison

Question

I am working on a jQuery/Javascript app where performance is really important.

What would be the fastest way in getting a number value from the following code? Is the same execution time for each cases or does it matter?

//Case 1
var number = $("#someID").css("left").slice(0, -2)/100; // Returns a number

//Case 2
var number= new String($("#someID").css("left").slice(0, -2)/100); // Returns a number

//Case 3
var number = $("#someID").css("left").slice(0, -2)/100;
var number = new String(number); // Returns a number

If you're doing this over and over again, it might be a good idea to do something completely different: keep the current "left" value for each object in a separate map. Then you don't have to slice it out of the string every time you need it. — Pointy
– Pointy, Commented Jul 21, 2010 at 19:51
If you need performance, don’t use jQuery but plain JavaScript: document.getElementById("someID").style.left.slice(0, -2)/100 — Gumbo
– Gumbo, Commented Jul 21, 2010 at 19:53
This is in a loop. Each time something is dragged the script will take that element left value and do several calculations with it. How can I put it in a map? — Mircea
– Mircea, Commented Jul 21, 2010 at 19:53
Oh well if there's some other code controlling "left" value then that might not work so well. — Pointy
– Pointy, Commented Jul 21, 2010 at 20:05

Sjoerd · Accepted Answer · 2010-07-21 19:53:28Z

0

Use the profiling functionality of Firebug to find the hotspots, and which solution is the fastest.

answered Jul 21, 2010 at 19:53

Sjoerd

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