Static class field allows colon value with no assignment

[TrueWill]

🔎 Search Terms

static

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about static

⏯ Playground Link

https://www.typescriptlang.org/play?#code/MYGwhgzhAEBiD29oG8BQ0PQgFzNglsNAEZgBOAXNNmQK4CmA3KgL6qrDwB2E8I9AOhDwA5gAoE8AaTIBKRtAD0i6LS4ATegDN8XeutRA

💻 Code

class Foo {
    static bar: true;
}

console.log(Foo.bar); // undefined

🙁 Actual behavior

I spotted this in production code.

The developer intended to write

class Foo {
    static bar = true;
}

which makes sense. TypeScript gives no errors or warnings with the colon-value. While you can use a colon to specify a type when assigning a value, that does not seem to be what is happening here. I can see no reason why anyone would intentionally write the original code.

🙂 Expected behavior

TypeScript reports an error.

Additional information about the issue

No response

[fatcerberus]

This technically may not a bug but a missing feature. In any case, duplicate of #27899.

[fatcerberus]

I can see no reason why anyone would intentionally write the original code.

It can sometimes make sense to write code like this, if you intend to do the actual initialization in a static block:

class Foo {
    static bar: boolean;
    static {
        this.bar = isBar();
    }
}

Note that true is a valid literal type; in fact boolean is equivalent to true | false.

[TrueWill]

Closing as duplicate.