microsoft / microsoft/TypeScript
Can't use async arrow function in/before super call
@rbuckton is already working on this.
Since Feb 5, 2021.
- Dominant language
- Go
- Stars
- 111k
- Forks
- 14.3k
- Avg merge
- 2d 4h
- Merged PRs (30d)
- 132
Description
Bug Report
🔎 Search Terms
super async arrow function this
🕗 Version & Regression Information
This only occurs using a target version of ES2016 or lower.
⏯ Playground Link
💻 Code
This works:
class A {
constructor(fn: () => Promise<void>) {
fn();
}
}
class B extends A {
constructor() {
super(async function () {
console.log("Hello");
});
}
}
new B();
This doesn't:
class A {
constructor(fn: () => Promise<void>) {
fn();
}
}
class B extends A {
constructor() {
super(async () => {
console.log("Hello");
});
}
}
new B();
The difference between the examples is the use of an arrow function vs a traditional function.
🙁 Actual behavior
It compiles crashes however at runtime with this error message:
ReferenceError: Must call super constructor in derived class before accessing 'this' or returning from derived constructor
The error lies in the generated __awaiter function trying to access this. The traditional function wraps the __awaiter call (therefore binding its own this) not causing it to fail.
🙂 Expected behavior
Print Hello to the console.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Assessment
This issue has not been assessed yet.