Brainfuck interpreter [Work in progress]

brainfuck.js

function brainLuck(code, input){
  
  function matchingBracket(code, instPtr){
    var count = 1;
    while(count > 0){
      var c = code[++instPtr];
      if(c === '[') count++;
      else if(c === ']') count--;
    }
    return instPtr;
  }
  
  function memMgmt(mem, memPtr, nb){
    var base = mem[memPtr];
    if(base === undefined)
      base = 0;
    var temp = base + nb;
    
    if(temp > 255) return (temp % 255) - 1;
    else if(temp < 0) return 256 + temp;
    else return temp;
  }
  
  var starts = [];
  function startCond(mem, memPtr, instPtr){
    if(mem[memPtr] === 0){
      return matchingBracket(code, instPtr);
    }else{
      starts.push(instPtr);
      return instPtr;
    }
  }
  function endCond(mem, memPtr, instPtr){
    if(mem[memPtr] !== 0){
      return starts[starts.length - 1];
    }else{
      starts.pop();
      return instPtr;
    }
  }
  
  var mem = [];
  var memPtr = 0;
  
  var inputPtr = 0;
  var ret = [];
  
  for(var i=0; i < code.length; i++){
    var cmd = code[i];
    
    switch(cmd){
      
      case ">":
        memPtr++;
        break;
      case "<":
        memPtr--;
        break;
      
      case "+":
        mem[memPtr] = memMgmt(mem, memPtr, 1);
        break;
      case "-":
        mem[memPtr] = memMgmt(mem, memPtr, -1);
        break;
        
      case ".":
        ret.push(String.fromCharCode(mem[memPtr]));
        break;
      case ",":
        mem[memPtr] = input[inputPtr++].charCodeAt(0);
        break;
        
      case "[":
        i = startCond(mem, memPtr, i);
        break;
      case "]":
        i = endCond(mem, memPtr, i);
        break;  
    }    
  }
  return ret.join("");
}