String Literal issue with function overloads

[folini]

TypeScript Version:

TypeScript 1.8.30.0

Issue

The following code (copy & paste from the TypeScript documentation) doesn't work. It generates a compiler error.

function createElement(tagName: "img"): HTMLImageElement;
function createElement(tagName: "input"): HTMLInputElement;
function createElement(tagName: string): Element;
// ... more overloads ...

function createElement(tagName: string): Element {
    // ... code goes here ...
}

While, just moving the most general signature at the tip of the list will compile correctly.

function createElement(tagName: string): Element;
function createElement(tagName: "img"): HTMLImageElement;
function createElement(tagName: "input"): HTMLInputElement;
// ... more overloads ...

function createElement(tagName: string): Element {
    // ... code goes here ...
}

[Arnavion]

What you have in the OP has no error (well, except for a missing return in the function body).

The code in the handbook does not have the tagName: string overload, which does result in TS2382: Specialized overload signature is not assignable to any non-specialized signature.. Is that what you meant?

(Using npm 1.8.10 which I believe corresponds to VS 1.8.30.0)

[yuit]

The example doesn't produce an error as @Arnavion points out. We made a change to such behavior. The behavior is in the "typescript@next".

[folini]

Thanks @Arnavion and @yuit for taking the time to answer my question.

Apparently I changed the code when I copy & pasted removing the issue.
The issue appears when there is no declaration of the non-specialized signature, and there is only the implementation. This is the original code listed in the documentation that generates an error:

Code generating the error

function createElement(tagName: "img"): HTMLImageElement;
function createElement(tagName: "input"): HTMLInputElement;
// ... more overloads ...

function createElement(tagName: string): Element {
    // ... code goes here ...
    return;
}

Code with no error

function createElement(tagName: "img"): HTMLImageElement;
function createElement(tagName: "input"): HTMLInputElement;
function createElement(tagName: string): Element;
// ... more overloads ...

function createElement(tagName: string): Element {
    // ... code goes here ...
    return;
}

[sandersn]

This was fixed in #6075.