How to prevent assiging similar types?

Question

How do I prevent TypeScript from allowing assigning similar but different types to a declared variable?

Consider following classes:

class Pe         


        

Answer 1

So it works by design (you can't escape it). From the official documentation:

Classes work similarly to object literal types and interfaces with one exception: they have both a static and an instance type. When comparing two objects of a class type, only members of the instance are compared. Static members and constructors do not affect compatibility.

class Animal {
    feet: number;
    constructor(name: string, numFeet: number) { }
}

class Size {
    feet: number;
    constructor(numFeet: number) { }
}

var a: Animal;
var s: Size;

a = s;  //OK
s = a;  //OK