Javascript: Sort array and return an array of indicies that indicates the position of the sorted elements with respect to the original elements

var test = ['b', 'c', 'd', 'a'];
var test_with_index = [];
for (var i in test) {
    test_with_index.push([test[i], i]);
}
test_with_index.sort(function(left, right) {
  return left[0] < right[0] ? -1 : 1;
});
var indexes = [];
test = [];
for (var j in test_with_index) {
    test.push(test_with_index[j][0]);
    indexes.push(test_with_index[j][1]);
}

Edit

You guys are right about for .. in. That will break if anybody munges the array prototype, which I observe annoyingly often. Here it is with that fixed, and wrapped up in a more usable function.

function sortWithIndeces(toSort) {
  for (var i = 0; i < toSort.length; i++) {
    toSort[i] = [toSort[i], i];
  }
  toSort.sort(function(left, right) {
    return left[0] < right[0] ? -1 : 1;
  });
  toSort.sortIndices = [];
  for (var j = 0; j < toSort.length; j++) {
    toSort.sortIndices.push(toSort[j][1]);
    toSort[j] = toSort[j][0];
  }
  return toSort;
}

var test = ['b', 'c', 'd', 'a'];
sortWithIndeces(test);
alert(test.sortIndices.join(","));

I would just fill an array with numbers 0..n-1, and sort that with a compare function.

var test = ['b', 'c', 'd', 'a'];
var len = test.length;
var indices = new Array(len);
for (var i = 0; i < len; ++i) indices[i] = i;
indices.sort(function (a, b) { return test[a] < test[b] ? -1 : test[a] > test[b] ? 1 : 0; });
console.log(indices);

Dave Aaron Smith is correct, however I think it is interesting to use Array map() here.

var test = ['b', 'c', 'd', 'a'];
// make list with indices and values
indexedTest = test.map(function(e,i){return {ind: i, val: e}});
// sort index/value couples, based on values
indexedTest.sort(function(x, y){return x.val > y.val ? 1 : x.val == y.val ? 0 : -1});
// make list keeping only indices
indices = indexedTest.map(function(e){return e.ind});