Prevent assigning to readonly property-CodePudding

Is there a way to fail the compilation of the code like in the example below:

interface Ro {
    readonly x: string;
}

const modify = (rw: {x: string;}) => rw.x = 'bye';
const use = (v: Ro) => {
    console.log(v.x);

    //v.x = 'bye'; Compiler error: "Cannot assign to 'x' because it is a read-only property."
    modify(v);// No errors, not even warnings.
}
const ro: Ro = {x: "hi"}
use(ro);
console.log(ro.x);// readonly field has been changed!

CodePudding user response：

There is not a way to fail the compilation currently. There are a few things you can do alternatively:

Use a lint rule
Use the technique suggested here which is pretty awkward: Disable allowing assigning Readonly types to non-readonly types
Be satisfied with a run-time error using Object.freeze

CodePudding user response：

Here:

const modify = (rw: {x: string;}) => rw.x = 'bye';

you're telling TypeScript to be more lenient than it should be. If you typed the argument correctly const modify = (rw: Ro) => //..., it would correctly disallow modification.

If we want, we can pretty much always bypass TypeScript safeguards and type checks, by writing things like like myVariable as unknown as any, or Object.defineProperty etc. It's not bulletproof.

CodePudding user response：

Probably the only way to achieve this is to use Object.freeze on the entire object.

Note: this will only apply at run time, the compilation will succeed