You can use this : http://jsbeautifier.org/
But it depends on the minify method you are using, this one only formats the code, it doesn't change variable names, nor uncompress base62 encoding.
edit: in fact it can unpack "packed" scripts (packed with Dean Edward's packer : http://dean.edwards.name/packer/)
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…