How can i add a readonly attribute to a declarations file?

Question

I'm creating a declarationsfile for a library that doesnt exist yet, but there are some classes in there that have readonly attributes. How can i put that in the declaration?

Answer 1

Strangely, you can't specify getters and setters on interfaces or on ambient declarations.

The closest you can get is:

interface Test {
    Prop: number;
}

class Example implements Test {
    private prop: number;

    get Prop() :number {
        return this.prop;
    }
}

Unfortunately, this doesn't prevent the implementation from allowing a setter and in the context of an ambient declaration it wouldn't prevent the caller from attempting to set the value.

Answer 2

With TypeScript 2.0 you can now declare readonly properties, for example

interface Point {
    readonly x: number;
    readonly y: number;
}

var p1: Point = { x: 10, y: 20 };
p1.x = 5;                            // Error, p1.x is read-only

var p2 = { x: 1, y: 1 };
var p3: Point = p2;                  // Ok, read-only alias for p2
p3.x = 5;                            // Error, p3.x is read-only
p2.x = 5;                            // Ok, but also changes p3.x because of aliasing

see here for more details.