Simple loop compilation

loopcompiler.js

function iterator(f, bindings) {
    
  bindings = bindings || {};

  var matches = f.toString().match(/function[^(]*\(\s*(\w+)\s*\)[^{]*(.*)/);

  if (!matches) {
    console.log("iterator function has wrong format, please use only one argument");
  }  

  var compiled,
      k,
      funStr = [],
      argNames = [],
      argValues = [],
      argName = matches[1],
      body = matches[2];
  
  for(k in bindings) {
    if (bindings.hasOwnProperty(k)) {
      argNames.push(k);
      argValues.push(bindings[k]);
    }
  }

  function freshName(name) {
    if (bindings.hasOwnProperty(name))
      return freshName("_" + name);
    return name;
  }

  var arrName = freshName("els"),
      counterName = freshName("i"),
      lengthName = freshName("length");

  funStr.push("(function(", argNames.join(','), ")", "{",
    "return function(",arrName,") { ",
      "var ", counterName ,",", 
              lengthName, "=", arrName,".length,", 
              argName, ";", 
      "for(",counterName,"=0;",counterName,"<",lengthName,";",counterName,"++) {", 
        argName, "=",arrName,"[",counterName,"];", 
        body,
      "}",
    "}",
  "})"
   )

  var compiled = eval.call(this, funStr.join(''));
  
  return compiled.apply(this, argValues);
}

use.js

var printAll = iterator(function(el) {
  console.log(el);
});

printAll([1,2,3]);
// yields:
//   1
//   2
//   3

// the closed environment has to be specified explicitly
var printClosure = iterator(function(el) {
  console.log(el + a);
}, {
  a: 5
});

printClosure([1,2,3]);
// yields
//   6
//   7
//   8

I didn't perform a representative empirical study, but a quick test (with a list of 100,000 elements) suggests that the compiled version is about 30 times faster then using jQuery's $.each.