var user = {}; now I want to create a setUsers() method that takes a key/value pair object and initializes the user variable.
setUsers = function(data) { // loop and init user } where data is like:
234: "john", 23421: "smith", .... 
3 Answers
Beware of properties inherited from the object's prototype (which could happen if you're including any libraries on your page, such as older versions of Prototype). You can check for this by using the object's hasOwnProperty() method. This is generally a good idea when using for...in loops:
var user = {}; function setUsers(data) { for (var k in data) { if (data.hasOwnProperty(k)) { user[k] = data[k]; } } } 
2 Comments
streetlight
Is there anyway to do this without a for in loop? I'm worried about speed through large key value pairs (and I know that Crockford isn't a fan from using JSLint, but I'm not sure of his reasoning). Is there a reason to worry about these things?
Tim Down
@streetlight: It depends on the environment. If you can rely on having ECMAScript 5 (all modern browsers do, as does Node.js), you have options such as
Object.keys(). If you need to support IE <= 8, for example, you're stuck with for...in.for (var key in data) { alert("User " + data[key] + " is #" + key); // "User john is #234" } 
Comments
Something like this:
setUsers = function (data) { for (k in data) { user[k] = data[k]; } } 
{{},..}. When would I use this one instead of an array of objects[{},..]? ok, here is the answer, welcome to SO;).