gleam-lang/gleam
Invalid TypeScript Declarations for property named `constructor` and other javascript keywords
Closed
#5,613 opened on Apr 16, 2026
good first issuehelp wantedhigh priority
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Description
Given this gleam code:
pub type Box {
Box(constructor: Int)
}
And this gleam.toml:
name = "app"
version = "1.0.0"
target = "javascript"
[dependencies]
gleam_stdlib = ">= 0.44.0 and < 2.0.0"
[dev_dependencies]
gleeunit = ">= 1.0.0 and < 2.0.0"
[javascript]
typescript_declarations = true
The generated typescript declarations are invalid with the following error:
Similarly when you use other property names such as prototype or then, the generated typescript declarations are valid, however do not match the generated JavaScript classes.
For example:
pub type Box {
Box(prototype: Int)
}
export class Box extends $CustomType {
constructor(prototype) {
super();
this.prototype$ = prototype;
}
}
export class Box extends _.CustomType {
/** @deprecated */
constructor(prototype: number);
/** @deprecated */
prototype: number;
}
Here the typescript autocompletion would suggest box.prototype even though it should be box.prototype$.
Maybe this is not important, because they are deprecated, but wanted to bring it up anyways.
This is on gleam 1.15.4