Get the key of an associative array

Question

I'm currently fetching an array with .each:

$.each(messages, function(key,message){ doStuff(); });

But the key is the index of the array and not the associative key.

How can I get it easily?

Answer 1

JavaScript doesn't have "associative arrays". It has arrays:

[1, 2, 3, 4, 5]

And objects:

{a: 1, b: 2, c: 3, d: 4, e: 5}

Array's don't have "keys". They have indices, which are counted starting at 0.

Arrays are accessed using [], and objects can be accessed using [] or ..

Example:

var array = [1,2,3];
array[1] = 4;
console.log(array); // [1,4,3]

var obj = {};
obj.test = 16;
obj['123'] = 24;
console.log(obj); // {test: 16, 123: 24}

If you try to access an array using a string as a key instead of an int, that may cause problems. You would be setting a property of the array and not a value.

var array = [1,2,3];
array['test'] = 4; // This doesn't set a value in the array
console.log(array); // [1,2,3]
console.log(array.test); // 4

jQuery's $.each works with both of these. In the callback for $.each, the first parameter, key, is either the object's key, or the array's index.

$.each([1, 2, 3, 4, 5], function(key, value){
    console.log(key); // Logs 0 1 2 3 4
});

$.each({a: 1, b: 2, c: 3, d: 4, e: 5}, function(key, value){
    console.log(key); // Logs 'a' 'b' 'c' 'd' 'e'
});

Answer 2

var data = {
    val1 : 'text1',
    val2 : 'text2',
    val3 : 'text3'
};
$.each(data, function(key, value) {
    alert( "The key is '" + key + "' and the value is '" + value + "'" );
});
​

See the Demo