Creating a TypeScript type that allows for the possibility of being undefined

I have a project where I am converting Scala code to TypeScript.

In Scala, there is a predefined type called Option which can either be a specific type or undefined.

In TypeScript, we usually represent it like this:

var myVar : MyType | undefined = await methodCall(...)

The methodCall function may look something like this:

function methodCall(...) : Promise<MyType | undefined>
{
   ........
   // The function body
}

Now, I am trying to find a way in TypeScript to define a type similar to Scala's Options, for example:

Problem Statement:

MyTypeOption ... it can be of MyType or undefined

Any suggestions on how I can achieve this in TypeScript?

Currently, my TypeScript code looks like this:

var myVar : MyType | undefined = await methodCall(...)

function methodCall(...) : Promise<MyType | undefined>
{
   ........
   // The function body
}

Answer №1

To create a helper type that combines an arbitrary type with undefined, you can define it as follows:

type Option<T> = T | undefined;

const n: number = undefined; // Error: Type 'undefined' is not assignable to type 'number'.

const o: Option<number> = undefined; // Okay

type MyType = string;

type MyTypeOption = Option<MyType>;

async () => {
    var myVar = await methodCall();
    myVar.charAt(0); // Error: Object is possibly 'undefined'.
}

async function methodCall(): Promise<MyTypeOption> {
    return undefined;
}

Playground Link

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