Setting array in javascript

Question

Noob question. Setting array elements throws an error.

I get this error when I run the script: array1[user_id] is undefined.

array1 = new Array();
// the data variable I got from a JSON source
// using jQuery
$.each(data, function(i, item) {
 // Set variables
 user_id = item.post.user_id;
 user = item.post.user;
 price = item.post.price;
 if (array1[user_id]['user'] != user) {
 array1[user_id]['price'] = price;
 array1[user_id]['user'] = user;
 }
}

• Cudos: Well.. I am trying to make more sense of it now...
• Ruan Mendes: It's not that bad, Cudos is clearly trying to define nested objects and doesn't realize each sub-object needs to be initialized independently.
• Cudos: @pst I am trying my best. I don't know about you but English is not my first language and javascript is pretty new to me. No reason to be rude.
• Ruan Mendes: @pst: did the OP not explain that the problem was that array1[user_id] is undefined?

Answer 1

First, you should not use an array, if you need a hash map, use objects. In some languages, it's one thing, but in JS they're not.

When defining a nested object you have to define each level as an object.

var hash = {};
// the data variable I got from a JSON source
$.each(data, function(i, item) {
 // Set variables
 user_id = item.post.user_id;
 user = item.post.user;
 price = item.post.price;
 // Have to define the nested object
 if ( !hash[user_id] ) {
 hash[user_id] = {};
 }
 if (hash[user_id]['user'] != user) {
 hash[user_id]['price'] = price;
 hash[user_id]['user'] = user;
 } 
}

• Ivan: Who said anything about jQuery?
• Jared Farrish: @Ivan - Nobody, but it often times makes life eas(ier).
• Ruan Mendes: @Ivan: the poster did, I just modified his original posting so it would work, I didn't add any jQuery. Read before you post and downvote!
• Ivan: Ah, you're right. The poster should have mentioned it somewhere since I was thinking of a non-jquery solution.
• Ruan Mendes: @Ivan: What was the poster supposed to mention? I also can't stand people that use jQuery for every answer, but the question is clearly not about jQuery, it just uses jQuery as part of the example.

Answer 2

If I understand this question correctly, you have to initialize the first dimension of array1 first, like so:

array1[user_id] = {};

then you can do this:

array1[user_id]['user'] = 'whatever';

That is of course assuming your user_id is not undefined.

• Cudos: Problem is that I don't know what the "user_id" variable is before I loop through the "data" variable.
• Jared Farrish: Then I would use an object and try catch.