Can I Specify Parameter Type as One of Many Types Instead of Any Type in TypeScript?

Question

In a method declaration in TypeScript, the parameter could be of type array of strings, booleans, or numbers. Do I have to declare it as any[] or is there a way to limit the input type as on of these three types?

Answer 1

Typescript 1.4 introduced Union Types so the answer now is yes, you can.

function myFunc(param: string[] | boolean[] | number[]): void; 

Using other type than the ones specified will trigger a compile-time error.

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If you want an array of multiple specific types, you can use Union Types for that as well:

function myFunc(param: (string|boolean|number)[]): void; 

Note that this is different from what OP asked for. These two examples have different meanings.

Answer 2

This seems a bit old question, but anyway, I came across it, and missed this other answer that I bring.

From TypeScript 1.4 seems that it is possible to declare multiple possible types for a function parameter like this:

class UtilsClass {     selectDom(element: string | HTMLElement):Array<HTMLElement> {         //Here will come the "magic-logic"     } } 

This is because of the new TypeScript concept of "union-types".

You can see more here.