ThisType doesn't enforce type-checking Object.prototype.call

[mkermani144]

🔎 Search Terms

• ThisType
• ThisType and call

🕗 Version & Regression Information

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

⏯ Playground Link

https://www.typescriptlang.org/play/?ssl=8&ssc=40&pln=1&pc=1#code/MYewdgzgLgBAYiEAuGAVAFgSwqgngBwFMAeAbxgA8UwBXAWwCNCAnGAXwD4YAyGcgM0QAKAJTV6TVmxgBePgCgYMQSFEKlSgPSaYoSCAA2hAHQGQAcyFQsEY7hEBuGNpjEAtG5gtmIZoo3MhFA0zGAw1tjGFA7+bPJx8gggxirGwACGBgZC5LgoAEzsjs467p5gIF7MPsxAA

💻 Code

const Foo: ThisType<{ x: number }> & { foo(): number } = {
  foo() {
    // console.log(this.y); // <-- error
    return this.x;
  }
}

Foo.foo.call({ y: 2 }); // <-- no error

🙁 Actual behavior

The last line doesn't give an error.

🙂 Expected behavior

The last line should give an error.

Additional information about the issue

No response

[jcalz]

ThisType doesn't do what you think it does; it just gives a contextual type to object literals, it doesn't actually constrain it from the outside. You're probably looking for a this parameter instead:

const Foo: { foo(this: { x: number }): number } = {
  foo() {
    console.log(this.y); // <-- error
    return this.x; // okay
  }
}

Foo.foo.call({ y: 2 }); // <-- error

Playground link

[mkermani144]

Thanks for the quick reply @jcalz.

I know about this parameters, but my point here is that these features may conflict. In addition, when I use ThisType, I don't want to duplicate the this type for each of the functions in an object.

[RyanCavanaugh]

It's not a bug that ThisType doesn't do two different things at once

[mkermani144]

It's not a bug that ThisType doesn't do two different things at once

I understand. I'm not necessarily stating it's a bug. Maybe it's more like a new feature. By the way, I think it may benefit developers. Or maybe I'm wrong.

[typescript-bot]

This issue has been marked as "Question" and has seen no recent activity. It has been automatically closed for house-keeping purposes.