Douglas Crockford examines the need for minimising the size of JavaScript code and compares minification and obfuscation. Obfuscation has the side-effect of introducing bugs because it changes variable names. The recommended approach is minification along with GZip compression. Since JavaScript is sent along in source form, it is impossible to hide that from a determined hacker
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