How to append an object to array in javascript?

Question

Why is the array getting just the last object?

this.checkpoints = new Array();

this.checkpoint = new Object();
    this.checkpoint['lat'];
    this.checkpoint['lng'];

this.checkpoint['lat'] = 1;
this.checkpoint['lng'] = 1;
this.checkpoints.push(this.checkpoint);

this.checkpoint['lat'] = 2;
this.checkpoint['lng'] = 2;
this.checkpoints.push(this.checkpoint);

this.checkpoint['lat'] = 3;
this.checkpoint['lng'] = 3;
this.checkpoints.push(this.checkpoint);

console.log(this.checkpoints);

The result is wrong:

[Object { lat=3,  lng=3}, Object { lat=3,  lng=3}, Object { lat=3,  lng=3}]

But if I try without objects, it's OK:

this.checkpoints = new Array();

this.checkpoints.push(1);

this.checkpoints.push(2);

this.checkpoints.push(3);

console.log(this.checkpoints);

The result is:

[1, 2, 3]

Please, what am I missing? Thanks in advance!

It's because the pushing is reference based. It pushes this.checkpoint's address (reference), not it's value. — Raein Hashemi
– Raein Hashemi, Commented May 18, 2015 at 6:58
I wonder what this :this.checkpoint['lat']; this.checkpoint['lng']; do — Royi Namir
– Royi Namir, Commented May 18, 2015 at 6:59
@RoyiNamir It means you are assigning properties to the object with those names. — Raein Hashemi
– Raein Hashemi, Commented May 18, 2015 at 7:01
@RaeenHashemi it was not a question but pointing to a non code : i.imgur.com/bcVR8o6.png ( line 3 & 4 at OP's code) — Royi Namir
– Royi Namir, Commented May 18, 2015 at 7:02

Arun P Johny · Accepted Answer · 2015-05-18 06:58:19Z

4

Because you are just changing the property values of the same object. You need to create 3 different objects.

You can simplify it using Object Initializer

this.checkpoints = new Array();

this.checkpoints.push({
    lat: 1,
    lng: 1
});
this.checkpoints.push({
    lat: 2,
    lng: 2
});
this.checkpoints.push({
    lat: 3,
    lng: 3
});

console.log(this.checkpoints);

answered May 18, 2015 at 6:58

Arun P Johny

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Himesh Aadeshara · Accepted Answer · 2015-05-18 07:16:36Z

0

this.checkpoint = new Object();
    this.checkpoint['lat'];
    this.checkpoint['lng'];

this.checkpoint['lat'] = 1;
this.checkpoint['lng'] = 1;
this.checkpoints.push(this.checkpoint);

this.checkpoint['lat'] = 2;
this.checkpoint['lng'] = 2;
this.checkpoints.push(this.checkpoint);

this.checkpoint['lat'] = 3;
this.checkpoint['lng'] = 3;
this.checkpoints.push(this.checkpoint);

it only changes the checkpoint['lat'] , checkpoint['lng'] property of the checkpoints object so when you execute the

" console.log(this.checkpoints);" statement

it will display only the last changed property value and that is 3 for both ['lat'] and ['lng'] former values are overridden by last one.

answered May 18, 2015 at 7:16

Himesh Aadeshara

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