I have a stopwatch method that has several properties, I want no one to be able to access them from outside the class, I made them private, but it is still possible to access them and their value can be changed. what do I do?

class StopWatch {
    private duration: number = 0;
    private status: string = 'stopped';
    private currentTime: number = 0;
    start () {
        if (this.status == 'started') {
            throw new Error("already started!");
        }
        this.currentTime = Date.now();
        this.status = "started";
    }
    stop() {
        if (this.status == "stopped") {
            throw new Error("already stopped!");
        }
        this.duration = Date.now() - this.currentTime   this.duration;
        this.status = "stopped";
        console.log((this.duration / 1000).toFixed(1));
    }
    reset() {
        if (this.status == 'started') {
            this.stop();
        }
        this.duration = 0;
    }
}
const obj = new StopWatch();

CodePudding user response：

As pointed out by Hrusikesh in the question comments, TypeScript visibility modifiers are enforced only at compile time. At runtime, your class members are always accessible like any JavaScript object properties:

Like other aspects of TypeScript’s type system, private and protected are only enforced during type checking.

But there are now JavaScript class private features: just prefix the member name with a hash (#), and it will be truly "private", i.e. not accessible from outside the class, even after compilation, since it is enforced by JavaScript:

class StopWatch2 {
    #duration: number = 0;

    method() {
        console.log("method", this.#duration);
    }
}

const obj2 = new StopWatch2();
obj2.method();
// [LOG]: "method",  0 

console.log("obj2", obj2.#duration); // Error: Property '#duration' is not accessible outside class 'StopWatch2' because it has a private identifier.
// Does not even run!

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