Access object literal with typed variable in TypeScript does not work

Question

I'm translating Java code into TypeScript and I've come across something I can't understand. I've create here object literal name a and I manage to use it as associative array. Then I've define class Node and create variable name n, when I try to use the variable n as key to the associative array the tsc compiler fail with Illegal property access. If I convert n variable to kk variable of type any everything works.

Why is that?

var a = {}
a['a'] = 3
a[4] = 5

class Node {

}
var n:Node = new Node();
a[n] = 44;  <---- Illegal property access

var kk: any = n;
a[kk] = 55

Fenton · Accepted Answer · 2012-10-18 09:18:09Z

2

In this statement:

a[n] = 44;

a is an object.

n is an instance of the Node class.

So you are trying to use a class as the key to a property on the a object.

When you use kk, which is an any type, TypeScript will assume that you know what you are doing and will assume that it will be a string or number at runtime. This is really ignoring the problem.

You could use the type of the n variable, which is a string:

a[typeof n]

answered Oct 18, 2012 at 9:18

Fenton

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1 Comment

Ido Ran Over a year ago

I see. using typeof is not the answer. I have getId function on the Node class so I'll use n.getId(). I guess I just forgot it is javascript after all so there are no real associative array.

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