KaSGa KaSGa - 3 years ago 167
TypeScript Question

Reverse-Mapping for String Enums

I wanted to use string enums in typescript but I can't see a support for reversed mapping in it.
I have an enum like this:

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


and I need to use it like this:

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


and yes I don't know what is it there in
modeStr
string and I need it parsed to the enum or a fail at parsing in runtime if the string is not presented in the enum definition.
How can I do that as neat as it can be?
thanks in advance

Answer Source

We can make the Mode to be a type and a value at 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"

A more strict version:

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 this answer:

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
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