A simple BrainFuck Javascript interpreter

brainfuck.js

var BrainFuck = (function(){
	function getBracketsPair(code){
		var stack = [],
			bracket = [],
			start,
			i,l;

		for (i = 0, l = code.length; i < l; i++ ) {
			if (code[i] === '[') {
				stack.push(i);
			} else if (code[i] === ']') {
				start = stack.pop();
				if( start ){
					bracket.push({
						start: start,
						end: i
					});
				} else {
					throw new Error("Unpaired bracket");
				}
			}
		}
		if (stack.length) {
			throw new Error("Unpaired bracket");
		}

		return bracket;
	}

	function type(o){
		return Object.prototype.toString.call(o).toLowerCase().slice(8,-1)
	}

	function exec(code,input_str){
		var input = type(input_str) === 'string' ? input_str.split("") : input_str, // input array
			output = [], // output array
			ptr = 0, // memory pointer
			c_ptr = 0, // code ptr
			bracket = getBracketsPair(code), // bracket pairs
			memory = [0], // memory array
			l = code.length,
			token;

		while(c_ptr < l){
			token = code[c_ptr];

			switch(token){
				case '+':
					memory[ptr]++;
					break;
				case '-':
					memory[ptr]--;
					break;
				case '<':
					if (--ptr < 0){
						ptr = 0;
						memory.unshift(0);
					}
					break;
				case '>':
					if (memory[++ptr] === undefined) {
						memory.push(0);
					}
					break;
				case ',':
					try {
						memory[ptr] = input.shift().charCodeAt(0);					
					} catch (e) {
						throw Error("Wrong input");
					}
					break;
				case '.':
					output.push(memory[ptr]);
					break;
				case '[':
					if (memory[ptr] === 0) {
						c_ptr = bracket.filter(function(b){
							return b.start === c_ptr
						})[0].end - 1;
					}
					break;
				case ']':
					if (memory[ptr]) {
						c_ptr = bracket.filter(function(b){
							return b.end === c_ptr
						})[0].start - 1;
					}
					break;
				default:
					break;
			}
			c_ptr++;
		}

		return output.map(function(w){
			return String.fromCharCode(w);
		}).join("");
	}

	return exec;
})();