Branfuck Interpreter

brainfuck.js

function brainfuck(code,input){

    var pc = 0;
    var sysout = [];
    var sysin = input.split('').reverse();
    var ptr = 0;
    var data = [0];
    var size = code.length;
    var program = code.split('')
    var loops = [];

    function interpret(){
        while(pc < code.length){
            var opcode = program[pc];
            switch(opcode){
                case '<': left(); break;
                case '>': right(); break;
                case '+': inc(); break;
                case '-': dec(); break;
                case '.': write(); break;
                case ',': read(); break;
                case '[': loop(); break;
                case ']': check(); break;
                default: pc++;
            }
        }
        return sysout.join('');
    }

    function inc(){ data[ptr] = (data[ptr]+1) % 256; pc++; }
    function dec(){ data[ptr] = data[ptr]-1 >= 0 ? data[ptr]-1 : 255; pc++; }
    function write(){ sysout.push(String.fromCharCode(data[ptr])); pc++; }
    function read(){ data[ptr] = (sysin.pop() || '\u0000').charCodeAt(0) ; pc++; }
    function isfalse(){ return data[ptr] === 0; }
    function istrue(){ return !isfalse(); }
    function left(){ ptr = (ptr-1 >= 0) ? ptr-1 : 0; pc++; }
    function right(){
        if(++ptr >= data.length){
            data.push(0);
        }
        pc++;
    }
    function loop(){ istrue() ? loops.push(++pc) : skip(); }
    function skip(){
        var pending = 1;
        pc++;
        while(pc < code.length && pending > 0){
            if(program[pc] == '['){
                pending++;
            } else if(program[pc] == ']'){
                pending--;
            }
            pc++;
        }
    }
    function check(){
        if(istrue()){
            pc = loops.pop();
            loops.push(pc);
        } else {
            loops.pop();
            pc++;
        }
    }

    return interpret();
}