JavaScript Crusher

crush.js

// Copyright 2014 Geraint Luff
// MIT Licensed
function crush(code, searchLimit) {
	var originalCode = code;
	searchLimit = searchLimit || 15;
	var substitutions = [];
	
	var bannedChars = /[\r\n"'\\]/;
	for (var charNum = 32; charNum < 127; charNum++) { // ASCII printable ("safe") characters
		var char = String.fromCharCode(charNum);
		if (code.indexOf(char) !== -1 || bannedChars.test(char)) continue;

		// Find best replacement
		var sequences = {};
		for (var i = 0; i < code.length; i++) {
			for (var j = 2; i + j < code.length && j < searchLimit; j++) {
				var extract = code.substring(i, i + j);
				sequences[extract] = (sequences[extract] || 0) + 1;
			}
		}
		var bestScore = 0, bestSub = null;
		for (var extract in sequences) {
			var score = (JSON.stringify(extract).length - 2)*(sequences[extract] - 1) - 1;
			if (score > bestScore) {
				bestScore = score;
				bestSub = extract;
			}
		}

		if (bestSub) {
			substitutions.push([char, bestSub]);
			code = code.split(bestSub).concat(bestSub).join(char);
		}
	}
	
	var stringConstant = '"' + code.replace(/\\/g, '\\\\').replace(/"/g, "\\\"") + '"';
	var stringConstantAlt = "'" + code.replace(/\\/g, '\\\\').replace(/'/g, "\\'") + "'";
	if (stringConstantAlt.length < stringConstant.length) stringConstant = stringConstantAlt;
	
	var subChars = substitutions.map(function (pair) {
		return pair[0];
	}).join('');
	
	var newCode = 'c=' + stringConstant + ';';
	newCode += 'for(i=' + subChars.length + ';i--;)';
	newCode += 'c=c.split("' + subChars + '"[i]),c=c.join(c.pop());';
	newCode += 'eval(c);';
	
	return newCode;
}

Currently not quite as good as jscrush (or other projects based on a similar code-base), but I couldn't find any license information for that project, so I wrote my own.