Set property of a class using a variable

Question

Is something like this possible?

const propName = "x";

class A {
    static propName = 1
    // equivalent to static x = 1
}

A[propName] // evaluates to 1

or would it be (typeof A)[propName]?

For obvious reasons, this is not a duplicate of this question

@PatrickRoberts Did you read this question? It's completely different to what you marked as a duplicate... — Tobiq, Mar 04 '19 at 02:24
I read the question. There is no property named `x`, just a property named `propName`. So either `A.propName` or `const propName = "propName";` — Patrick Roberts, Mar 04 '19 at 02:25
@PatrickRoberts You should re-open this question. I have no idea why you think that other question is even related - it's not even TypeScript — Tobiq, Mar 04 '19 at 02:27
That is not equivalent to `static x = 1`, FYI. The meaning of `static propName = 1` does not change just because a string variable `propName` exists. — Patrick Roberts, Mar 04 '19 at 02:31

score 2 · Answer 1 · answered Mar 04 '19 at 02:33

2

This is possible, simply as:

const propName = "x";

class A {
    static [propName] = 1
    // equivalent to static x = 1
}

A[propName]

answered Mar 04 '19 at 02:33

Tobiq

1) Don't assume it's me downvoting. 2) `A[propName]` will compile regardless of whether `x` exists on `A` or not. Try it yourself. This is not type-safe, see [this](https://stackoverflow.com/q/43740513/1541563). – Patrick Roberts Mar 04 '19 at 02:34
[Yes](https://stackoverflow.com/search?q=user%3A1541563+%5Btypescript%5D) – Patrick Roberts Mar 04 '19 at 02:36
This answer is correct; it is using [computed properties](https://github.com/Microsoft/TypeScript/wiki/What's-new-in-TypeScript#computed-properties), which TypeScript understands as long as the value of the property is statically known as a literal type (so `let propName = "x";` would fail because `propName` would be `string`). – jcalz Mar 04 '19 at 13:42
And as for `A[propName]` compiling whether or not `x` exists on `A`: you would get a warning with `--strict` or `--noImplicitAny` modes. – jcalz Mar 04 '19 at 13:45

1 Answers1