Syntax Error on Destructuring Assignment in TypeScript

Question

interface User extends Function {
    player: number,
    units: number[],
    sites: string[],
}
class User extends Function {
    constructor() {
        super('return this.player')
        [this.player, this.units, this.sites] = getBelongings(); // Destructuring Assignment
        
    }
}
const me = new User();
function getBelongings(): [number, number[], string[]] {
    return [1, [1], ['1']]
}

Playground Link

The above seems nice, and I think my assignment has no problem.

But It says: Type 'string[]' cannot be used as an index type.(2538)

I tried destructuring some times before and now have no idea about what's wrong.

Is it a TypeScript problem or a wrong syntax? And how can I make it operate well? Thanks a lot.

Destructuring arrays works like so : const [a, b] = myFunction() — l -_- l
– l -_- l, Commented Jul 5, 2022 at 12:00
You need a semi colon after the call to super, or it's trying to run both statements together. The code reads as an index accessor to the return value from super, instead of a new statement. — Dave Meehan
– Dave Meehan, Commented Jul 5, 2022 at 12:05
This is weird code; you're extending Function and calling super("return this.player"). I very much doubt this will behave the way you intend at runtime, and TypeScript certainly has no idea what kind of function your instances of User will be. Very little of that has to do with destructuring assignment; maybe you could edit the question to make it a plain example of your issue, like this. — jcalz
– jcalz, Commented Jul 5, 2022 at 12:13

Dave Meehan · Accepted Answer · 2022-07-05 12:07:18Z

3

You need a semi colon after the call to super, or it's trying to run both statements together.

The code, as it stands, reads as an index accessor to the return value from super, instead of a new statement.

super('return this.player');   // <-- insert semi colon
[this.player, this.units, this.sites] = getBelongings();

answered Jul 5, 2022 at 12:07

Dave Meehan

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1 Comment

Radu Diță Over a year ago

Very good point, semicolon is not the only thing that fixes this, a comma would do the same, although it has different semantics

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