TypeScript Private Field

class DataContainer {
    // Private fields (declaration is mandatory before assignment)
    #internalId: string;
    #metadata = { initialized: true };

    constructor(id: string) {
        this.#internalId = id;
    }

    // Private accessor
    get #idLength(): number {
        return this.#internalId.length;
    }

    // Private method
    #validateId(): boolean {
        return this.#idLength > 0;
    }

    public process(): void {
        if (this.#validateId()) {
            // Accessible only within the class body
            console.log(`Processing: ${this.#internalId}`);
        }
    }
}

const container = new DataContainer("sys-01");
// container.#internalId; 
// TypeScript Error: Property '#internalId' is not accessible outside class 'DataContainer' because it has a private identifier.

class NetworkRequest {
    #requestToken: string;

    constructor(token: string) {
        this.#requestToken = token;
    }

    static isNetworkRequest(obj: any): obj is NetworkRequest {
        // Safely checks for the presence of the private field at runtime
        return #requestToken in obj;
    }
}

class PrivacyMechanics {
    private softPrivate: number = 1;
    #hardPrivate: number = 2;

    // 1. Constructor Parameter Properties
    // The 'private' keyword can automatically declare and assign a class field.
    // The '#' identifier CANNOT be used in parameter properties (results in a syntax error).
    constructor(private id: string) {
        // constructor(#id: string) // Syntax Error
    }
}

const instance = new PrivacyMechanics("test-id");

// 2. TypeScript 'private' modifier (Soft Privacy)
// Normal access fails at compile-time:
// instance.softPrivate; // TypeScript Error

// However, casting to 'any' bypasses the type checker, allowing successful runtime access:
console.log((instance as any).softPrivate); // Outputs: 1

// 3. ECMAScript '#' identifier (Hard Privacy)
// Normal access fails at compile-time:
// instance.#hardPrivate; // TypeScript Error

// Casting to 'any' still fails at compile-time for '#' identifiers:
// console.log((instance as any).#hardPrivate); 
// TypeScript Error: Property '#hardPrivate' is not accessible...

// Dynamic access attempts fail to retrieve the private value at runtime:
console.log((instance as any)['#hardPrivate']); // Outputs: undefined

// Conceptual representation of downleveled ES2015 emission
var _DataContainer_internalId = new WeakMap();

class DataContainer {
    constructor(id) {
        _DataContainer_internalId.set(this, void 0);
        _DataContainer_internalId.set(this, id);
    }
}