Interview question

What is method overriding and how does super work with it? Method overriding क्या है और super इसके साथ कैसे काम करता है?

Answer

Method overriding lets a subclass provide its own implementation of a method inherited from a parent class. The super keyword allows calling the parent's version from within the override.

class Employee {
    constructor(name, salary) {
        this.name = name;
        this.salary = salary;
    }

    getDetails() {
        return `${this.name}: $${this.salary}`;
    }

    calculateBonus() {
        return this.salary * 0.1; // default 10% bonus
    }
}

class Manager extends Employee {
    constructor(name, salary, teamSize) {
        super(name, salary);
        this.teamSize = teamSize;
    }

    // OVERRIDING getDetails - completely replaces parent behavior
    getDetails() {
        return `${super.getDetails()}, manages ${this.teamSize} people`;
        // super.getDetails() calls the PARENT's version, then extends it
    }

    // OVERRIDING calculateBonus with different logic entirely
    calculateBonus() {
        const baseBonus = super.calculateBonus(); // reuse parent's calculation
        const managerBonus = this.teamSize * 100; // add manager-specific bonus
        return baseBonus + managerBonus;
    }
}

const emp = new Employee('John', 50000);
console.log(emp.getDetails());      // John: $50000
console.log(emp.calculateBonus());  // 5000

const mgr = new Manager('Jane', 80000, 5);
console.log(mgr.getDetails());      // Jane: $80000, manages 5 people
console.log(mgr.calculateBonus());  // 8000 + 500 = 8500

// Constructor chaining - super() MUST be called before using 'this' in a subclass
class Base {
    constructor() { this.type = 'base'; }
}
class Derived extends Base {
    constructor() {
        // this.type = 'derived'; // ReferenceError if called before super()
        super(); // must come first
        this.type = 'derived'; // now safe to use 'this'
    }
}

Method overriding subclass को parent class से inherited method का अपना implementation देने देता है। super keyword override के अंदर से parent की version call करने देता है।

class Employee {
    constructor(name, salary) {
        this.name = name;
        this.salary = salary;
    }

    getDetails() {
        return `${this.name}: $${this.salary}`;
    }

    calculateBonus() {
        return this.salary * 0.1;
    }
}

class Manager extends Employee {
    constructor(name, salary, teamSize) {
        super(name, salary);
        this.teamSize = teamSize;
    }

    // getDetails OVERRIDE करना
    getDetails() {
        return `${super.getDetails()}, manages ${this.teamSize} people`;
    }

    // calculateBonus OVERRIDE करना
    calculateBonus() {
        const baseBonus = super.calculateBonus(); // parent का calculation reuse
        const managerBonus = this.teamSize * 100;
        return baseBonus + managerBonus;
    }
}

const emp = new Employee('John', 50000);
console.log(emp.getDetails());      // John: $50000

const mgr = new Manager('Jane', 80000, 5);
console.log(mgr.getDetails());      // Jane: $80000, manages 5 people
console.log(mgr.calculateBonus());  // 8500

// super() 'this' use करने से पहले call होना ज़रूरी है
class Base {
    constructor() { this.type = 'base'; }
}
class Derived extends Base {
    constructor() {
        super(); // पहले आना चाहिए
        this.type = 'derived';
    }
}

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