As web pages become more and more like applications, code performance becomes more and more important. This article looks at a number of performance issues to avoid, in EcmaScript, DOM and AJAX requests. Covers eval, the with keyword, try/catch in performance-critical code, global variables, implicit object conversion, string concatenation, primitive operations over function calls, repainting and reflowing documents, modifying elements, using XPath.
Dean Edwards takes Mozilla's newly introduced forEach method, and implements it for non-Mozilla browsers, for enumerating over objects and arrays.
A collection of performance related techniques, including temporary references (for deeply namespaced properties), optimising loops by referencing the collection length once, reasons to avoid the with syntax, using null over the delete function, comparison for equality and identity and short-circuit logical expressions
Ryan Campbell volume tests Prototype's each() Enumeration function and finds that although the code is more elegant than the for loops, the overhead is quite heavy, and the performance impact too high. The summary: If basic JavaScript will do the task, then use basic JavaScript