Why isn't TypeScript acknowledging my string literal declaration?

Below is the code snippet I am working with:

type Timeframe = "morning" | "afternoon" | "evening";

let myTimeframe: Timeframe = "morning";

const someValue: any = {time: "incorrect"};
myTimeframe = someValue.time;

console.log(myTimeframe);

I want myTimeframe to only be assigned the values morning, afternoon, or evening.

However, the console displays incorrect.

Is there a way to modify my code so that it triggers a compile time error whenever myTimeframe may not be one of morning, afternoon, or evening?

(When I try something like 

let myTimeframe: Timeframe = "incorrect"
, it does detect the error at compile time)

typescript

Answer №1

When you type something as any, it means it can be assigned to any other type and accessing any property is allowed, with the type being any.

It's generally recommended to avoid using any. If you have a type that is not known, consider using the more restrictive unknown (refer to here for more information on unknown vs any).

In this case, you can simply remove the any:

type Period = "day" | "month" | "year";

let myPeriod: Period = "day";

const anyValue = {period: "wrong"};
myPeriod = anyValue.period; //error will occur

console.log(myPeriod);

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