如何将字符串枚举转换为 Reactjs typescript 中的枚举？

Question

I have an enum like this in a .ts file:

export enum TimeOfDay{
    MORNING = "AM",
    NOON = "12noon",
    EVENING = "PM",
    MIDNIGHT = "12midnight"
}

In another .tsx file, I have a string "12noon" in a variable named selectedOption and I want to convert it into this enum. How can I do that?

I tried these based on the other answers in StackOverflow, but none of the worked:

var timeInDay: TimeOfDay = TimeOfDay[selectedOption];

The above is giving TS7053 error.

var timeInDay: TimeOfDay = <TimeOfDay>selectedOption;

The above is giving TS17008 and TS2604 errors.

var timeInDay: TimeOfDay = (<any>TimeOfDay)[selectedOption];

The above is giving TS2339 and TS17008 errors.

I've gone through many answers on this site but didn't find a solution.

Answer 1

Here are some ways to use a string where a string enum type is expected:

TS Playground

enum TimeOfDay{
  MORNING = "AM",
  NOON = "12noon",
  EVENING = "PM",
  MIDNIGHT = "12midnight"
}

function doSomethingWithTimeOfDay (time: TimeOfDay): void {
  console.log(time);
}

const selectedOption = '12noon';

// As you observed, this doesn't work:
doSomethingWithTimeOfDay(selectedOption);
//                       ~~~~~~~~~~~~~~
// Argument of type '"12noon"' is not assignable to parameter of type 'TimeOfDay'.

// Use a predicate to check at runtime:
function isTimeOfDay (value: string): value is TimeOfDay {
  return Object.values(TimeOfDay).includes(value as TimeOfDay);
}

if (isTimeOfDay(selectedOption)) {
  doSomethingWithTimeOfDay(selectedOption); // ok
}

// Or, if you're certain that the string is a valid string enum value,
// then you can use an assertion:
doSomethingWithTimeOfDay(selectedOption as TimeOfDay); // ok