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Can someone please help me. I have been writing javascript and jquery for over a year now, but there is one topic I have never run across. ARRAYS. can someone give me a basic idea on how arrays in javascript work and how I can use them. I am trying to store an array of arrays that contain strings. Like this

  • Base Array
    • [0] Sub Array
      • [0] 'Hello World'
      • [1] 'Hey What's Up World'
    • [1] Sub Array
      • [0] 'Hello America'
      • [1] 'Hello UK'

And I might also have some numeric values in there too. So, how can I go about this task.

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3 Answers 3

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var array = [
  ['Hello World', "Hey What's Up World"],
  ['Hello America', 'Hello UK'],
  [1, 2, 3]
];

array[0][1]; // "Hey What's Up World"
array[2][2]; // 3
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5 Comments

and how do I add elements to one of the internal arrays. var Like array = []; array[0] = ['hello world']; array[0][1] = 'Hey What's up world'; Main Question: Are the arrays mutable???
Arrays have a push() method which adds items to them. So to add a string to the first sub-array: array[0].push('new string');. Or you use an index 1 bigger than last index and just assign: array[0][2] = 'new string';. Or by using the length - 1 array[0][array[0].length - 1] = 'new string';. But push is usually the clearest.
thanks, let me try this out in conjunction with something else I need to do on my page. Thank You Stack Overflow and all of your great members
@squeegy - to add a new member, just use length, don't subract 1 as that will be the current last member (length is always one bigger than the highest index).
@RobG - durrrr yeah your right, not sure what I was thinking.
3

Like this:

var array = [
              [ 'Hello World', 'Hey What Up World' ],
              [ 'Hello America', 'Hello UK' ]
            ];
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1 Comment

and how do I add elements to one of the internal arrays. var Like array = []; array[0] = ['hello world']; array[0][1] = 'Hey What's up world'; Main Question: Are the arrays mutable???
1

keep in mind that Arrays in javascript can be both numeric and hash, as in...

var foo = new Array();
foo[0] = "a";
foo[1] = "b";

etc...

or 

foo["key1"] = "a";
foo["key2"] = "b";

The primary difference here is that if you use it in the hash context, you can't get a length (array.length) as it will always be 0. However, if you want to loop through your hash you can do it like this:

for(myKey in foo){
  ...
}

where mykey will take on the key and you can get the value by using foo[mykey], in the above loop.

You can also loop this way through a numeric array, in which case myKey will just run through all the numbers.

Lastly, if you arbitrarily stick something into a high numbered element as in...

foo = new Array();
foo[1000] = "what happened to the first 999";

0 - 999 will all be initialized to null, but the length of this array will now immediately be 1001;

As to adding multiple dimensions, since every item in the array is just an Object, it can hold whatever you want it to, including another Array.

Hope that helps.

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2 Comments

Better to say that Arrays are just plain objects with a special length property and some handy methods inherited from Array.prototype. There is nothing special about the numeric properties, they are just that: numeric properties of anotherwise (almost) plain JS object. "Indexes" are just numeric property names—they are strings, just like all other object property names. Finally, for..in should always be protected by a hasOwnProperty test else it will include inherited enumerable properties.
RobG, you're absolutely right, but I thought it would just be confusing to say "its just an object with a length property", since it's called "array" and most languages use arrays in a very specific manner (which applies here as well). So I thought I'd denote the most specific issue that a new comer to a Javascript array might encounter. Namely, the non innumerability of it, when it's indexed by something other than numbers.

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