How do I access properties of a javascript object if I don't know the names?

Question

Say you have a javascript object like this:

var data = { foo: \'bar\', baz: \'quux\' };

You can access the properties by the property name:

Answer 1

You can loop through keys like this:

for (var key in data) {
  console.log(key);
}

This logs "Name" and "Value".

If you have a more complex object type (not just a plain hash-like object, as in the original question), you'll want to only loop through keys that belong to the object itself, as opposed to keys on the object's prototype:

for (var key in data) {
  if (data.hasOwnProperty(key)) {
    console.log(key);
  }
}

As you noted, keys are not guaranteed to be in any particular order. Note how this differs from the following:

for each (var value in data) {
  console.log(value);
}

This example loops through values, so it would log Property Name and 0. N.B.: The for each syntax is mostly only supported in Firefox, but not in other browsers.

If your target browsers support ES5, or your site includes es5-shim.js (recommended), you can also use Object.keys:

var data = { Name: 'Property Name', Value: '0' };
console.log(Object.keys(data)); // => ["Name", "Value"]

and loop with Array.prototype.forEach:

Object.keys(data).forEach(function (key) {
  console.log(data[key]);
});
// => Logs "Property Name", 0