How to useConditional Type in Javascript
In this approach, we are using a conditional type to infer the return type from a tuple parameter. It deconstructs the tuple, extracting the last element as the return type, ensuring accurate type inference for functions with tuple parameters.
Example: We define myReturnType to infer the return type from a tuple parameter. It applies this to myFunction, then assigns the return value of booleanReturn() to a variable, result, with the inferred type.
type myReturnType<T extends any[]> = T extends
[infer First, ...infer Rest, infer Return] ? Return : never;
function myFunction(...args: [number, string, boolean]):
string {
return "w3wiki";
}
type Result = myReturnType<Parameters<typeof myFunction>>;
function booleanReturn(): boolean {
return true;
}
const result: Result = booleanReturn();
console.log(result);
Output:
true
How to Infer Return Type from a Tuple Parameter ?
In TypeScript, inferring the return type from a tuple parameter involves deriving the type of value returned by a function based on the types of its tuple parameters. This allows the compiler to deduce the functionâs output type without explicit annotation, enhancing type safety and readability.
These are the following approaches:
Table of Content
- Using Conditional Type
- Using ReturnType with Function Type
- Using Inference with Tuple Parameter
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