Looking for some help with my class method. Here is the current implementation:
handleTab<B extends boolean = false>(getIndex?: B): B extends true ? number : string {
return getIndex ? 1 : '';
}
Encountering an error message that says: Type 'string | number' cannot be assigned to type 'B extends true ? number : string'. Type 'number' cannot be assigned to type 'B extends true ? number : string'
Any insights on what I might be doing incorrectly? Thank you!
When it comes to generically typed parameters in TypeScript, there are no magic tricks (at least not yet). This results in the type of getIndex ? 1 : '' being string | number, rather than B extends true ? number : string. As a consequence, this mismatch with the function's return type leads to an error.
One approach to address this issue is by utilizing overloads:
function handleTab(getIndex?: false): string
function handleTab(getIndex: true): number;
function handleTab(getIndex?: boolean): string | number;
function handleTab(getIndex?: boolean): string | number {
return getIndex ? 1 : '';
}
An additional handleTab(getIndex?: boolean) ensures correct functionality even when passing a parameter of type boolean.
Alternatively, you can consolidate the signatures into one using overloads:
function handleTab<B extends boolean = false>(getIndex?: B): B extends true ? number : string;
function handleTab(getIndex?: boolean): string | number {
return getIndex ? 1 : '';
}
However, both of these examples don't verify if the returned expression aligns with the provided overloads. For instance, returning just 1 would not trigger any complaints.
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