Reasonably fast implementation of Lempel–Ziv–Welch compression

lzw.js

lzw = {
	decode: function (str) {
		var i, code, phrase,
			dict = {},
			chr = str[0],
			last = chr,
			out = [chr],
			next = 256;
		for (i = 1; i < str.length; i++) {
			code = str[i].charCodeAt(0);
			phrase = code < 256 ? str[i] : (dict[code] ? dict[code] : (last + chr));
			out.push(phrase);
			dict[next++] = last + (chr = phrase[0]);
			last = phrase;
		}
		return out.join('');
	},
	encode: function (str) {
		var chr, i,
			dict = {},
			out = [],
			phrase = str[0],
			code = 256;
		for (i = 1; i < str.length; i++) {
			chr = str[i];
			if (dict[phrase + chr] != null) {
				phrase += chr;
			} else {
				out.push(phrase.length > 1 ? dict[phrase] : phrase.charCodeAt(0));
				dict[phrase + (phrase = chr)] = code++;
				phrase = chr;
			}
		}
		out.push(phrase.length > 1 ? dict[phrase] : phrase.charCodeAt(0));
		return String.fromCharCode.apply(0, out);
	},
	encodeObject: function (obj) {
		return this.encode(JSON.stringify(obj));
	},
	decodeObject: function (str) {
		return JSON.parse(this.decode(str));
	}
}