JavaScript array indexes

Question

I am using Angular1x and I simply want to create an array object with numeric indexes:

var unreadMessagesCookieObject = [];

unreadMessagesCookieObject[id] = {
     id: messageObj.id,
     lastNotified: moment.getTime()
};

All fine? Well no not really:

(6) [null, null, null, null, null, {…}]
0: null
1: null
2: null
3: null
4: null
5:
id: 1
lastNotified: 1601769147988

Why do I have an object with 5 null indexes. I want to write the Object to a cookie but not the 5 null values.

How can I create an array object with an arbitrary numeric index. Note that I cannot use 0 as my first index since I want to be able to search in the array object by an id.

Does this answer your question? Why does a new javascript array have 'undefined' entries? — Ivar
– Ivar, Commented Oct 4, 2020 at 0:10
Is this the result of a round trip through JSON? Anyway, it looks like you probably want an object (= {}), not an array (= []). — Ry-
– Ry- ♦, Commented Oct 4, 2020 at 0:15

Barremian · Accepted Answer · 2020-10-04 07:30:12Z

1

JS arrays are already list-like objects. Instead of trying to overwrite it's behavior I'd tell you to create a standard JS object instead.

let unreadMessagesCookieObject = Object.create(null);

unreadMessagesCookieObject[id] = {
   id: messageObj.id,
   lastNotified: moment.getTime()
};

Working snippet:

let unreadMessagesCookieObject = Object.create(null);

unreadMessagesCookieObject[5] = {
  id: 1,
  lastNotified: 1601769147988
};

console.log(unreadMessagesCookieObject);

answered Oct 4, 2020 at 7:30

Barremian

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