How to add an empty array to object?

Question

I'm having trouble adding my empty array into my object via the bracket notation method. I know how to get my empty array into the object via dot notation, but I just don't understand why the bracket notation isn't working for me.

Update: I understand my problem now; the context switch between dot notation & bracket notation blinded me & I completely failed to recall that in my 3rd block - animal[noises] (forgot the "") was trying to access the property value of the property noises, which I hadn't created yet in my object

Creating & adding properties to my object

var animal = {};
animal.username = "Peggy";
animal["tagline"] = "Hello";

Which will then create this:

animal {
      tagline: "Hello",
      username: "Peggy"
}

Why won't the following work when I'm trying to add it into my object?

var noises = [];
animal[noises];

I'm getting this in my console (same as above):

animal {
      tagline: "Hello",
      username: "Peggy"
}

I was able to get my result this way:

animal.noises = [];

Which outputs this into my console:

animal {
  noises: [],
  tagline: "Hello",
  username: "Peggy"
}

But that still leaves me with the question: why doesn't this work via bracket notation?

`animal[noises];` means you are trying to access an attribute of `animal` with the name given by `noises`. You are not creating any attribute there. — thefourtheye, Jan 17 '15 at 16:27
I just updated the question. Take a look at the 3rd code block — Clifford Fajardo, Jan 17 '15 at 16:33
@CliffordFajardo that doesn't change anything. You didn't expect `animal["Hello"];` to create a property called `tagline` with the value `Hello`, did you? Now why would you expect that `animal[[]]` (which is effectively your attempt) should create a property named `noises`? You clearly have no idea about the meaning of bracket notation, for what you should look it up in a beginner JavaScript tutorial. — The Paramagnetic Croissant, Jan 17 '15 at 16:37

score 2 · Accepted Answer · answered Jan 17 '15 at 16:27

2

Use

animal.noises = noises;

or

animal['noises'] = noises;

As when you are using animal[noises]; it means when you are trying to read data from the object.

answered Jan 17 '15 at 16:27

Satpal

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Thank you. I also failed to recall that with bracket notation I need "" around noises. Your response was succinct & clear. – Clifford Fajardo Jan 17 '15 at 17:02

score 1 · Answer 2 · answered Jan 17 '15 at 16:32

1

For animal[noises],

animal is the object
and noises is the key/property of the object animal

And an array cannot be a key. If you want to put noises array in animal object you can do it as follows,

animal['noises'] = noises;

answered Jan 17 '15 at 16:32

Kelsadita

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score 1 · Answer 3 · edited May 23 '17 at 11:43

1

In your case you have to try

animal['noises']=noises

Array [] notation is used to get property of an object that requires a quote around it. Array notations are commonly used to get identifiers of objects having special characters included.say,

   var animal={
      "@tiger":'carnivore' // you can't have @tiger without quote as identifier
   } 
  console.log(animal.@tiger) // it will give ERROR
  console.log(animal['@tiger']) // it will print out  'carnivore'

this link has good explanation on array and dot notation .

edited May 23 '17 at 11:43

Community

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answered Jan 17 '15 at 16:34

AL-zami

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Thank you for the great, concise example! – Clifford Fajardo Jan 17 '15 at 17:09

How to add an empty array to object?

3 Answers3