Creating nested objects in TypeScript

Question

What's the easiest way to make nested objects in TypeScript? I want to be able to add elements in nested objects like this:

let dictionary: { [key: string]: { [key: string]: number  }  } = {};
dictionary['x']['y'] = 2
dictionary['x']['z'] = 5

I expect:

console.log(dictionary['x'])  // -> {'y': 2,'z': 5}

console.log(dictionary['x']['y'])  // -> 2

Start with `dictionary['x'] = {}`? Unless you use e.g. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy the inner objects won't magically appear. — jonrsharpe, Oct 26 '22 at 16:14
Related: [JavaScript: Write to dictionary if key doesn't exist](https://stackoverflow.com/q/67107996) — VLAZ, Oct 26 '22 at 16:16
Yeah, this looks like a duplicate of that one to me. Note that you could always write `(dictionary.x??={}).y = 2` as a one-liner, if you must — jcalz, Oct 26 '22 at 16:28

score 1 · Accepted Answer · answered Oct 26 '22 at 16:16

1

What's happening is that you are assigning the value 2 to the object at dictionary['x'], which resolves to undefined.

Try to initialise dictionary['x'] = {} first.

answered Oct 26 '22 at 16:16

toanphan19

1 Answers1