What's the difference between objects and associated array in javascript?

Question

The Confusing discussion

In this question, there is a discussion on the concepts of associated array and object in javaScript which I got a bit confused.

In this example code:

var check = {
  pattern : {
    name: /^[a-zA-Z-\s]{1,20}$/,
    email: /^[a-zA-Z0-9._(-)]+@[a-zA-Z0-9.(-)]+\.[a-zA-Z]{1,4}$/,
    pass: /.{6,40}/,
    url:  /^[(-)\w&:\/\.=\?,#+]{1,}$/,
    aml:  /<(.+)_([a-z]){1}>$/
    }
};

Here is the discussion makes me confused:

@steven.yang the outer object is not an associative array in your sample, but that is what is being asked for

@sissonb what do you mean by 'outer object is not an associative array'? I think associated array is expressed as object in javascript. The difference is in the notation - either through foo.bar or foo[bar]

@steven.yang associated array means key => value. http://en.wikipedia.org/wiki/Associative_array Your inner object has a key of pattern, the object containing this associative array has no key.

My Understanding of Associated Array and Objects in JS

Associated array is defined as key-value pairs which is expressed as the object in JavaScript.

The outer object assigned to check has a key pattern and an value of another object. The inner object has keys of name, email ... and corresponding values of regular expression objects.

Could both objects be counted as associative arrays?

Answer 1

Not really, here's why:

var arr = new Array();
arr["foo"] = 100;
arr["bar"] = 200;
console.log(arr.length); // Prints 0.

Adding elements to an associative array should increase its length (IMO).

It looks and acts (somewhat) like an associative array because of syntactic sugar. What appear to be "array entries", however, are (just) object properties.

Answer 2

If you define "associative array" as a data structure that stores information as a collection of key-value pairs, then yes, JavaScript objects are associative arrays.

However, the phrase "associative array" is not generally used in the context of JavaScript, rather, we say "object". I'd suggest sticking to standard JS terminology to avoid misunderstandings.

Note that JS also has (non-associative) arrays, with elements accessed via numeric indexes. These are also objects and so allow non-numeric key properties, but this is generally considered bad practice.