Is [x,y,z].join('') really faster than x + y + z for strings?

Question

Is [x,y,z].join('') really faster than x + y + z for strings?

Under the impression that join() is faster, I started through my code to use it rather than +, then I ran into the following line in the Google Analytics code:

    ga.src = ('https:' === document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';

Assuming the Google coders are among the most knowledgeable, it makes me wonder. Of course, that line is only going to run once per page load, and one could say that any speed difference is negligible. But still?

Answer 1

The Array .join() method (-trick) for concatenating strings has its roots back then when websites ran on Internet Explorers like a lot. For IE6 + 7 its very true than .join() is much faster than using the + operator due to a really bad behavior with string operations in IE.

For other browsers the performance difference wasn't that big, so it was good advice to use .join() (again, back then). Nowadays, most engines optimize string operations big time and unless you think any of your code runs in IE6+7 a lot, you should just use +.

Answer 2

Using Firebug Console in Firefox 6.0.2 using the following code:

b = new Date().getTime(); for (var i = 0; i < 10000; i++) {a = "sfhfdshdshsdh" + "sfhsfdhsfhdsfh" + "shsfdsdgsdgsgsdfgdfsgsfdghsdfhsdh";} c = new Date().getTime(); d = c - b;

and

b = new Date().getTime(); for (var i = 0; i < 10000; i++) {a = ["sfhfdshdshsdh","sfhsfdhsfhdsfh","shsfdsdgsdgsgsdfgdfsgsfdghsdfhsdh"].join();} c = new Date().getTime(); d = c - b;

I average in the low 40s for "+" and low 50s for "join" so it seems join is slower. This is most likely because of the need to create an array for join. Also this may be different in different browsers with different interpreters.

Answer 3

Here is an example which I ran on google chrome.

Try some other broswers....

In chrome for me + was always faster...

http://jsperf.com/join

http://jsperf.com/join-6