JS Beautifier is online too for deobfuscating complex JavaScript code. Paste the code in the Input box, hit Control + Enter and the code will start making sense.

The beautifier can reformat bookmarklets for reading as well as unpack scripts that were originally packed by Dean Edward’s popular packer before distribution.

JS Beautifier is on Github and there are quite a few Chrome extensions, Firefox add-ons, bookmarklets and command-line tools that make use of this tool to unpack JavaScript.