Use string literals for the TypeScript enum values

Let's say that we have the following TypeScript enum:

enum Theme {
    DEFAULT,
    LIGHT,
    DARK,
}

If you don't set the values for enum, they will be set to incremental numbers by default.

So `Theme.DEFAULT`, `Theme.LIGHT` and `Theme.DARK` will take the value of 0, 1, 2, respectively. It is more hard to debug:

console.log(Theme.DARK); // 2

Even if we set the number for enum values, it is still possible for us to set an invalid value for a variable whose type is the enum:

enum Theme {
    DEFAULT = 0,
    LIGHT = 1,
    DARK = 2,
}

// TypeScript doesn't throw errors
const theme: Theme.DEFAULT = 3;

Due to these reasons, it's advised to use string literals for the enum values. The `Theme` enum should look like as follow:

enum Theme {
    DEFAULT = 'Default',
    LIGHT = 'Light',
    DARK = 'Dark',
}

console.log(Theme.DARK);                // 'Dark'
let theme: Theme.DEFAULT = 'Default';   // ERROR

Use short-circuits conditionals

Use template literal to concatenate strings