Property with getter: This condition will always return 'false'

[blaumeise20]

Bug Report

🔎 Search Terms

• getter condition

🕗 Version & Regression Information

• This seems like intended behavior (it is sometimes, but not in this case)

⏯ Playground Link

Playground link with relevant code

💻 Code

class Example {
  private get _foo() {
    return Math.random() < 0.5 ? "a" : "b";
  }

  bar() {
    if (this._foo === "a") {
      console.log("got 'a'");
      // this error should not occur:
      if (this._foo === "b") {
        console.log("lucky case, got 'b' too");
      }
    }
  }
}

class Span {
  get end() { return this.start + this.length }
  constructor(public start: number, public length: number) {}
}

const span = new Span(4, 2);

if (span.end == 6) {
  span.length += 1;
  // same here:
  if (span.end == 7) {
    console.log("worked");
  }
}

🙁 Actual behavior

An error occured because TypeScript thinks this._foo/span.end doesn't change until that if-check, but in these examples it does.

🙂 Expected behavior

There shouldn't be such checks with getters.

[MartinJohns]

Another duplicate of #9998.

[fatcerberus]

For the record: TypeScript makes no distinction between getters and plain properties at the type level.

[typescript-bot]

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