In TypeScript, How to cast boolean to number, like 0 or 1

As we know, the type cast is called assertion type in TypeScript. And the following code section:

// the variable will change to true at onetime
let isPlay: boolean = false;
let actions: string[] = ['stop', 'play'];
let action: string = actions[<number> isPlay];

On compiling, it go wrong

Error:(56, 35) TS2352: Neither type 'boolean' nor type 'number' is assignable to the other.

Then I try to use the any type:

let action: string = actions[<number> <any> isPlay];

Also go wrong. How can I rewrite those code.

You can’t just cast it, the problem is at runtime not only at compile time.

You have a few ways of doing that:

let action: string = actions[isPlay ? 1 : 0];
let action: string = actions[+isPlay];
let action: string = actions[Number(isPlay)];

Those should be fine with both the compiler and in runtime.

You can convert anything to boolean and then to a number by using +!!:

const action: string = actions[+!!isPlay]

This can be useful when for example you want at least two out of three conditions to hold, or exactly one to hold:

const ok = (+!!something)  + (+!!somethingelse) + (+!!thirdthing) > 1
const ok = (+!!something)  + (+!!somethingelse) + (+!!thirdthing) === 1

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