I'm currently working with a complex AJAX control (Grid), and I have to concatenate a lot of strings (HTML) to render them on the client side with JavaScript. In JavaScript, each string is immutable (like .NET), and this means that every time the engine concatenates a string using + or +=, it creates a new instance of string and disposes the old one. This, in some browsers (mainly Internet Explorer), makes the concatenation very slow. In other browsers like Mozilla Firefox or Safari, these concatenations are optimized before getting executed (JavaScript engine in Firefox 3 is absolutely amazing!!!).
