How to implement class constants?

TypeScript 2.0 has the readonly modifier:

class MyClass {
    readonly myReadOnlyProperty = 1;

    myMethod() {
        console.log(this.myReadOnlyProperty);
        this.myReadOnlyProperty = 5; // error, readonly
    }
}

new MyClass().myReadOnlyProperty = 5; // error, readonly

It’s not exactly a constant because it allows assignment in the constructor, but that’s most likely not a big deal.

Alternative Solution

An alternative is to use the static keyword with readonly:

class MyClass {
    static readonly myReadOnlyProperty = 1;

    constructor() {
        MyClass.myReadOnlyProperty = 5; // error, readonly
    }

    myMethod() {
        console.log(MyClass.myReadOnlyProperty);
        MyClass.myReadOnlyProperty = 5; // error, readonly
    }
}

MyClass.myReadOnlyProperty = 5; // error, readonly

This has the benefit of not being assignable in the constructor and only existing in one place.