String concatenation vs string buffers in Javascript

Question

I was reading this book - Professional Javascript for Web Developers where the author mentions string concatenation is an expensive operation compared to using an array to s

Answer 1

I actually have some experience in this area, since my primary product is a big, IE-only webapp that does a LOT of string concatenation in order to build up XML docs to send to the server. For example, in the worst case a page might have 5-10 iframes, each with a few hundred text boxes that each have 5-10 expando properties.

For something like our save function, we iterate through every tab (iframe) and every entity on that tab, pull out all the expando properties on each entity and stuff them all into a giant XML document.

When profiling and improving our save method, we found that using string concatention in IE7 was a lot slower than using the array of strings method. Some other points of interest were that accessing DOM object expando properties is really slow, so we put them all into javascript arrays instead. Finally, generating the javascript arrays themselves is actually best done on the server, then you write then onto the page as a literal control to be exectued when the page loads.