Object instance from string literal Typescript

Question

I will often make a string literal like this

type stringNumbers = 'One' | 'Two' | 'Three';

And use it in a class constructor

class myClass {
    display: stringNumbers;
    constructor(display: stringNumbers) {
        this.display = display;
    }
}

My problem is when I create a new class. My value is types how I would like it but I have to enter a string for display like this.

let newMyClass = new MyClass('Two');

This is fine for simple objects, vscode will show what types I can use but there isn't any intellisense, And gets very messy when you have anything more advanced.

What I would like to have is an enum or object with properties named the same as the string literal and whose value is the string value like this

enum nums = {
    One,
    Two,
    Three
}

or

let nums = {
    One: 'One';
    Two: 'Two';
    Three: 'Three';
}

That way when I make a new class I can do this

let newMyClass = new MyClass(nums.One);

Any advice on how to make these class declarations better? I love the string literal types but they become almost as useless as just setting it to a string type on complex objects. In my use case I want to bind a form field to a property on a model, but that is in the middle of a bunch of other options for a field so the tooltips are very cluttered.

Nitzan Tomer · Accepted Answer · 2017-03-03 21:18:46Z

2

If you want to use an enum then:

enum nums {
    One,
    Two,
    Three
}

class myClass {
    display: nums;

    constructor(display: nums) {
        this.display = display;
    }
}

new myClass(nums.One);

If you want to use the enum but want to have the string value (name) and not the ordinal then:

class myClass {
    display: string;

    constructor(display: nums) {
        this.display = display[display];
    }
}

If you want to use the object and pass a key as string:

let nums = {
    One: 'One',
    Two: 'Two',
    Three: 'Three'
}

type keys = keyof typeof nums;

class myClass {
    display: string;

    constructor(display: keys) {
        this.display = nums[display];
    }
}

new myClass("One");

answered Mar 3, 2017 at 21:18

Nitzan Tomer

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