Reverse matching for strings

Question

I wanted to use string enumerations in typescript, but I don't see support for displaying back in it. I have an enumeration like this:

enum Mode {
    Silent = "Silent",
    Normal = "Normal",
    Deleted = "Deleted"
}

and I need to use it as follows:

let modeStr: string;
let mode: Mode = Mode[modeStr];

and yes, I don’t know what it is there in the string modeStr, and I need it to deal with the enumeration or crash during parsing at runtime if the string is not present in the enumeration definition. How can I do this as carefully as possible? thank you in advance

Answer 1

We can make a Modetype and a value of the same type.

type Mode = string;
let Mode = {
    Silent: "Silent",
    Normal: "Normal",
    Deleted: "Deleted"
}

let modeStr: string = "Silent";
let mode: Mode;

mode = Mode[modeStr]; // Silent
mode = Mode.Normal; // Normal
mode = "Deleted"; // Deleted
mode = Mode["unknown"]; // undefined
mode = "invalid"; // "invalid"

:

type Mode = "Silent" | "Normal" | "Deleted";
const Mode = {
    get Silent(): Mode { return "Silent"; },
    get Normal(): Mode { return "Normal"; },
    get Deleted(): Mode { return "Deleted"; }
}

let modeStr: string = "Silent";
let mode: Mode;

mode = Mode[modeStr]; // Silent
mode = Mode.Normal; // Normal
mode = "Deleted"; // Deleted
mode = Mode["unknown"]; // undefined
//mode = "invalid"; // Error

String Enum as :

enum Mode {
    Silent = <any>"Silent",
    Normal = <any>"Normal",
    Deleted = <any>"Deleted"
}

let modeStr: string = "Silent";
let mode: Mode;

mode = Mode[modeStr]; // Silent
mode = Mode.Normal; // Normal
//mode = "Deleted"; // Error
mode = Mode["unknown"]; // undefined

Answer 2

Proxies, :

stringEnum.ts

export type StringEnum<T extends string> = {[K in T]: K}
const proxy = new Proxy({}, {
  get(target, property) {
    return property;
  }
})
export default function stringEnum<T extends string>(): StringEnum<T> {
  return proxy as StringEnum<T>;
}

:

import stringEnum from './stringEnum';
type Mode = "Silent" | "Normal" | "Deleted";
const Mode = stringEnum<Mode>();

Answer 3

, , - :

let reverseMode = new Map<string, Mode>();
Object.keys(Mode).forEach((mode: Mode) => {
    const modeValue: string = Mode[<any>mode];
    reverseMode.set(modeValue, mode);
});

, let mode: Mode = reverseMode.get('Silent');

: , , TSLint ...

Edit: I originally write Mode[mode], but then TS can throw TS7015 on this line, so I added a listing.