bf.js

function bf (code) {
  var codeSize = code.length;
  var i = 0, ip = 0, cp = 0, dp = 0, m = {};

  var loopIn = {}, loopOut = {};
  var tmp = [];
  for ( var cp = 0; cp < codeSize ; cp++ )
      if ( code[cp] == '[' )
          tmp.push(cp);
      else
          if ( code[cp] == ']' )
              loopOut[loopIn[cp] = tmp.pop()] = cp;

  for (var cp = 0; cp < codeSize && i < 100000; cp++, i++) {

      switch(code[cp]) {

          case '>': dp++; break;
          case '<': dp--; break;
          case '+': m[dp] = ((m[dp]||0)+1)&255; break
          case '-': m[dp] = ((m[dp]||0)-1)&255; break;
          case '.': console.log(String.fromCharCode(m[dp])); break;
          case ',': m[dp] = prompt('input').charCodeAt(ip++)||0; break;
          case '[': m[dp]||(cp=loopOut[cp]); break;
          case ']': cp = loopIn[cp]-1; break;
      }
  }  
}