How can I define an object based array in TypeScript?

Question

In Javascript, I can define a collection using an object, something like this:

var myArray = {};
myArray['some-key1'] = new CustomObject('param1');
myArray['some-key2'] = new CustomObject('param2');
myArray['some-key3'] = new CustomObject('param3');

In TypeScript, can I have a collection based on object's properties, like in Javascript?

Another question, if I have 100 elements in one collection, what would be faster - storing these items in a classic array (myarray.push(instanceObj)), or storing them as properties of objects?

Use Map class, see stackoverflow.com/questions/37894517/…

Pavel Gatnar
– Pavel Gatnar

2016-12-21 20:18:04 +00:00
Commented Dec 21, 2016 at 20:18 — Pavel Gatnar
– Pavel Gatnar, Commented Dec 21, 2016 at 20:18
Another option is to have a object with subobjects.

Thomas Juranek
– Thomas Juranek

2016-12-21 20:23:12 +00:00
Commented Dec 21, 2016 at 20:23 — Thomas Juranek
– Thomas Juranek, Commented Dec 21, 2016 at 20:23
var myArray: {[key: string]: CustomObject} = {}

Pavel Gatnar
– Pavel Gatnar

2016-12-21 20:31:15 +00:00
Commented Dec 21, 2016 at 20:31 — Pavel Gatnar
– Pavel Gatnar, Commented Dec 21, 2016 at 20:31

thedayturns · Accepted Answer · 2016-12-22 22:29:54Z

1

If you have a fixed number of keys, the best thing to do is:

const myObject = {
    "some-key1": new CustomObject("param1"),
    "some-key2": new CustomObject("param2"),
    "some-key3": new CustomObject("param3"),
}

Note that now even something like this typechecks:

myObject["some-key1"] // TypeScript correctly infers the type to be CustomObject!

If you can't do that, the best way is to use an index type:

let myObject: { [key: string]: CustomObject };

which indicates to TypeScript that myObject maps strings to CustomObjects.

Another question, if I have 100 elements in one collection, what would be faster - storing these items in a classic array (myarray.push(instanceObj)), or storing them as properties of objects?

It really depends on what you're planning to do with the array/object. What's your use case?

edited Dec 22, 2016 at 22:29

answered Dec 21, 2016 at 22:33

thedayturns

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