Node JS - Object Value Update Strange Behavior

Question

I have a simple object I'm trying to modify and the results are puzzling. This is executed in node.js.

I have an object as follows:

var element = {  
  ident: "value",
  green:
    { date: value2,
      key: value3,
      key2: value4,
      key3: 
       { id1: 
         { p1: [],
           p2: [],
           p3: [],
           p4: [] },
       { id2: 
         { p1: [],
           p2: [],
           p3: [],
           p4: [] },
       { id3: 
         { p1: [],
           p2: [],
           p3: [],
           p4: [] } } },
  red:
    { date: value5,
      key: value6,
      key2: value7,
      key3: 
       { id1: 
         { p1: [],
           p2: [],
           p3: [],
           p4: [] },
       { id2: 
         { p1: [],
           p2: [],
           p3: [],
           p4: [] },
       { id3: 
         { p1: [],
           p2: [],
           p3: [],
           p4: [] } } } };

When I try to set the value of a single "p2" to an array i've filled with some data, each "p2" for that color is set, not just the one referenced. I'm setting the value like so:

element[green].key3[id1][p2] = someArray;

everything in brackets are variables pointing to the key name. The output of the above sets 3 values... all the ids of Green - green.key3.id1.p2, .id2.p2 and .id3.p2 all to the value I only want for green.key3.id1.p2

Any ideas as to what might be happening here? Thanks in advance for the help.

Answer 1

How are you building this object? It may be that you've assigned the same empty array to every p2 in a colour. When you do that each p2 will be a reference to the same array, so pushing a value into one will apparently push that value into each. To test if these are references to the same array, check:

green.key3.id1.p2 === red.key3.id2.p2

if this gives you true , then what I said above is the case. Essentially this is like:

var a = [];
var b = a;
var c = a;

b.push(1); // b = [1], c = [1];
b === c; // true, since they are really references to the same object (array).

EDIT

After rereading, it may be that actually id1 , id2 etc. are assigned to the same object. ie

var id = { p1: [], p2: [], p3: [] };
green.key3.id1 = id;
green.key3.id2 = id;

Like the above, you can test if this is the case by doing:

// true if these are really references to the same object.
green.key3.id1 === green.key3.id2;

If you want a quick way to reuse code without this behavior, then you can do:

function Id() {
    this.p1 = [];
    this.p2 = [];
    this.p3 = [];
}

green.key3.id1 = new Id();
green.key3.id2 = new Id();

Each new Id() will be a new object.