Getting a list of associative array keys

Question

Try this:

var keys = [];
for (var key in dictionary) {
  if (dictionary.hasOwnProperty(key)) {
    keys.push(key);
  }
}

hasOwnProperty is needed because it's possible to insert keys into the prototype object of dictionary. But you typically don't want those keys included in your list.

For example, if you do this:

Object.prototype.c = 3;
var dictionary = {a: 1, b: 2};

and then do a for...in loop over dictionary, you'll get a and b, but you'll also get c.

for (var key in dictionary) {
  // Do something with key
}

It's the for..in statement.

You can use: Object.keys(obj)

Example:

var dictionary = {
  "cats": [1, 2, 37, 38, 40, 32, 33, 35, 39, 36],
  "dogs": [4, 5, 6, 3, 2]
};

// Get the keys
var keys = Object.keys(dictionary);

console.log(keys);

See reference below for browser support. It is supported in Firefox 4.20, Chrome 5, and Internet Explorer 9. Object.keys() contains a code snippet that you can add if Object.keys() is not supported in your browser.

Just a quick note. Be wary of using for..in if you use a library (jQuery, Prototype, etc.), as most of them add methods to created Objects (including dictionaries).

This will mean that when you loop over them, method names will appear as keys. If you are using a library, look at the documentation and look for an enumerable section, where you will find the right methods for iteration of your objects.

Simple jQuery way:

This is what I use:

DictionaryObj being the JavaScript dictionary object you want to go through. And value, key of course being the names of them in the dictionary.

$.each(DictionaryObj, function (key, value) {
    $("#storeDuplicationList")
        .append($("<li></li>")
        .attr("value", key)
        .text(value));
});