JavaScript dynamic array with object and array

Question

I have a problem with creating list with objects in JavaScript: the object is going to contain an Integer value and an array.

The structure will look like this (this code works):

var list = [ {
 id : 1234,
 dependencyList : [ {
 id : 2142
 }, {
 id : 5313
 } ]
 }, {
 id : 4312,
 dependencyList : [ {
 id : 2142
 }, {
 id : 5313
 } ]
 } ];

The problem is that I want to create this list dynamically, in other words something like this:

var list = [];
var object;
object.id=1234;
object.dependencyList = [];
object.dependencyList.push(2222);
list.push(object);

This code does not work when I try to alert(list[0].length) and it returns 0 and after using JSON.stringify(list) it only returns [[]].

Anyone know a solution for this?

• Grundy: list[0] is object not an array, in your sample list[0] == { id : 1234, dependencyList : [ { id : 2142 }, { id : 5313 } ] }
• megawac: var object = {}; ???
• Grundy: yep, @megawac, trying set property to undefined object
• Tibos: Unrelated: Seems to me that your list could look better as a map of arrays: list = { 1234 : [ 2142, 5313], 4312 : [2142, 5313] };
• dag roger stokland rui: var object = {}; solved it! Thank you!

Answer 1

list[0] is an object and not an array, which is why you're not seeing anything for length. Try:

console.log(Object.keys(list[0]).length);

Or you could even just console.log(list[0]) and check your console to ensure that it contains something.

Also, I assume you meant:

var object = {};

Because otherwise object is undefined and your script won't work. Another thing you will have to change is:

object.dependencyList.push(2222);

to:

object.dependencyList.push({id: 2222});

• dag roger stokland rui: var list = []; var object = {}; object.id=4444; object.dependencyList = []; object.dependencyList.push({id:2222}); list.push(object)
• Rob Baillie: @dag-roger-stokland-rui Not sure why this isn't voted as the answer, though the one that contains half of this answer is...
• dag roger stokland rui: Yes, i agree. This answer is more detailed.

Answer 2

Object isn't defined. Do:

var object = {};

• Rob Baillie: Though be aware the structure won't be the same as the one you describe, it'll be var list = [ { id : 1234, dependencyList : [ 2142, 5313 ] }, { id : 4312, dependencyList : [ 2142, 5313 ] } ]

Answer 3

You should do list[0].dependencyList.length) also you shoud change: object.dependencyList.push(2222); for object.dependencyList.push({id: 2222});

Answer 4

Objects are your friend.

If you need to create a lot of these things, you should probably define how they are shaped in a function. An advantage of this is that you can then create a setter for adding a dependency that hides the implementation as a push against a particular member variable.

Something like this:

function createObject( id ) {
 var object = {};
 object.id = id;
 return object;
}
function createObjectWithDependencies( id ) {
 var object = createObject( id );
 object.dependencyList = [];
 object.addDependency = function( dependentObject ) {
 object.dependencyList.push( dependentObject );
 }
 return object;
}
var list = [];
var object = createObjectWithDependencies( 1234 );
object.addDependency( createObject( 2142 ) );
object.addDependency( createObject( 5313 ) );
list.push( object );
var object = createObjectWithDependencies( 4312 );
object.addDependency( createObject( 2142 ) );
object.addDependency( createObject( 5313 ) );
list.push( object );
console.log( list );