What's the most efficient way to turn an object's keys to its lowercase version

JavaScript performance comparison

Revision 9 of this test case created by João Jerónimo

Info

http://stackoverflow.com/questions/12539574/whats-the-best-way-most-efficient-to-turn-all-the-keys-of-an-object-to-lower

Preparation code

 
<script>
Benchmark.prototype.setup = function() {
    var obj = {
      "SomeThing": 2,
      "OthErThing": 9,
      "AnotherThing": 10000,
      "OhAndOneMoreThing": 193013923,
      "aQuiteLargeStringaQuiteLargeStringaQuiteLargeString": 29320381,
      "SomeThing2": 2,
      "OthErThing2": 9,
      "AnotherThing2": 10000,
      "OhAndOneMoreThing2": 193013923,
      "aQuiteLargeStringaQuiteLargeStringaQuiteLargeString2": 29320381,
      "SomeThing3": 2,
      "OthErThing3": 9,
      "AnotherThing3": 10000,
      "OhAndOneMoreThing3": 193013923,
      "aQuiteLargeStringaQuiteLargeStringaQuiteLargeString3": 29320381,
      "SomeThing4": 2,
      "OthErThing4": 9,
      "AnotherThing4": 10000,
      "OhAndOneMoreThing4": 193013923,
      "aQuiteLargeStringaQuiteLargeStringaQuiteLargeString4": 29320381,
      "SomeThing5": 2,
      "OthErThing5": 9,
      "AnotherThing5": 10000,
      "OhAndOneMoreThing5": 193013923,
      "aQuiteLargeStringaQuiteLargeStringaQuiteLargeString5": 29320381
    }
};
</script>

Test runner

Warning! For accurate results, please disable Firebug before running the tests. (Why?)

Java applet disabled.

Testing in unknown unknown
Test Ops/sec
joaojeronimo's function
var keys = Object.keys(obj);
var n = keys.length;
while (n--) {
  var key = keys[n];
  if (key !== key.toLowerCase()) {
    obj[key.toLowerCase()] = obj[key]
    delete obj[key]
  }
}
pending…
Don't check if the key is already in lower case
// Might be cheaper to just change it, but I doubt it
var keys = Object.keys(obj);
var n = keys.length;
while (n--) {
  var key = keys[n];
  obj[key.toLowerCase()] = obj[key]
  delete obj[key]
}
pending…
moonwave99
var keys = Object.keys(obj);
var n = keys.length;
var lowKey;
while (n--) {
  var key = keys[n];
  if (key === (lowKey = key.toLowerCase())) continue

  obj[lowKey] = obj[key]
  delete obj[key]

}
pending…
var keyLower;
for (var key in obj) {
  keyLower = key.toLowerCase();
  if (keyLower != key) {
    obj[keyLower] = obj[key];
    delete obj[key];
  }
}
pending…
kennebec
    Object.keys(obj).forEach(function(key){
        var k=key.toLowerCase();
        if(k!= key){
            obj[k]= obj[key]
            delete obj[key];
        }
    });
pending…

Compare results of other browsers

Revisions

You can edit these tests or add even more tests to this page by appending /edit to the URL. Here’s a list of current revisions for this page:

0 comments

Add a comment