Ordering

Don’t put more general overloads before more specific overloads:

/* WRONG */
declare function fn(x: any): any;
declare function fn(x: HTMLElement): number;
declare function fn(x: HTMLDivElement): string;
 
var myElem: HTMLDivElement;
var x = fn(myElem); // x: any, wat?

Do sort overloads by putting the more general signatures after more specific signatures:

/* OK */
declare function fn(x: HTMLDivElement): string;
declare function fn(x: HTMLElement): number;
declare function fn(x: any): any;
 
var myElem: HTMLDivElement;
var x = fn(myElem); // x: string, :)

Why: TypeScript chooses the first matching overload when resolving function calls. When an earlier overload is “more general” than a later one, the later one is effectively hidden and cannot be called.

Links:

https://www.typescriptlang.org/docs/handbook/declaration-files/do-s-and-don-ts.html#ordering

doc_TypeScript

2025-01-10 15:47:30

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