I will have several objects with the same property names, e.g.
const a = {foo: 111,};
const b = {foo: 222,};
So I’d like to have a global type for them, e.g.
type T = {foo: number,};
// in another file
const a: T = {foo: 123,};
But those objects are supposed to be constant, i.e. their values should not change since the time of their declaration. Is it possible to enforce such thing? So that
let a: T = {foo: 123,};
// or
const a = {foo: 123,};
a.foo = 321;
would throw an error.
Is it possible? Something like this:
//this is a syntax error
type T = {foo: number,} as const;
Thank you.
>Solution :
Use the readonly property modifier:
type T = { readonly foo: number };
// ~~~~~~~~
const a: T = { foo: 123 };
a.foo = 321; // error on a.foo
If you have multiple properties, you can use the Readonly utility type:
type T = Readonly<{ foo: number }>;
// ~~~~~~~~
const a: T = { foo: 123 };
a.foo = 321; // error on a.foo