TypeScript doesn’t properly handle a constructor with a quoted name

[j-f1]

TypeScript Version: 3.5.0-dev.20190418

Search Terms: typescript quoted constructor

Code

class Foo {
    constructor(name: string) {
      this.name = name
    }
}
class Bar {
    "constructor"(name: string) {
      this.name = name
    }
}

new Foo("hello")
new Bar("hello")

Expected behavior:
Compiles without error

Actual behavior:
The new Foo call compiles properly, but the new Bar call produces a type checking error:

test.ts:9:9 - error TS2554: Expected 0 arguments, but got 1.

9 new Bar("hello")
          ~~~~~~~

Note that running the code (with the type assertions stripped) results in both constructors being called, but TypeScript’s ES5 transpilation instead sets the second constructor as a method named constructor, which causes it not to be run.

Playground Link: Open playground ↗️

Related Issues: Encountered in https://github.com/prettier/prettier/issues/6063.

[MartinJohns]

The second code snippet does not create a constructor, it creates a property named constructor.

If you expect otherwise, then how would you expect to be able to define a property with that name?

edit: Tho it seems that in JavaScript it works as you expect it. Really weird.

[jcalz]

Issues #3841 (see comment) and #5989 (see comment) might be related in that they use this syntax as a workaround so that class instances could have strongly typed constructor properties.

[RyanCavanaugh]

We guessed wrong what the ES class semantics would be, which is pretty unfortunate now.

Not clear how to proceed since this will be a runtime breaking change for people who chose their method/property names extremely poorly.

[RyanCavanaugh]

Plan: Issue an error in 3.5 if we see this and target is <= ES5, then change the ES5 emit in 3.6.

[andrewbranch]

Plan: Issue an error in 3.5 if we see this and target is <= ES5, then change the ES5 emit in 3.6.

Moving the milestone since the grammar error part is done. This issue now tracks

change the ES5 emit