Unable to add generic function overload for module default export

[saschanaz]

TypeScript Version: 3.5.0-dev.20190508

Search Terms: module add overload

Code

// nanohtml.d.ts
export default function<T extends HTMLElement = HTMLElement>(strings: TemplateStringsArray, ...keys: any[]): T;

// @ts-check
// index.js
// install nanohtml@1.6.1
const nanohtml = require("nanohtml");

/** @type {HTMLAnchorElement} */
const a = nanohtml`<a href="example.com">Example</a>`;

Expected behavior:

a should be HTMLAnchorElement.

Actual behavior:

Error: Type 'HTMLElement' is missing the following properties from type 'HTMLAnchorElement': ...

[MartinJohns]

You don't specify the type for T, and there is no argument that allows the compiler to infer the type from, so the compiler falls back to the default type for T which is HTMLElement.

If you specify the type then it works.

nanohtml<HTMLAnchorElement>`<a href="example.com">Example</a>`

Not a bug, works as intended.

[saschanaz]

@MartinJohns Two things:

1. The example is in JavaScript with checkJs. Sorry to provide no such indication.
2. Even then, you don't have to explicitly give T. Try it yourself

declare function generic<T extends HTMLElement = HTMLElement>(num: number): T;

var x: HTMLAnchorElement = generic(1);