Interview question

What is the difference between instance methods and static methods regarding prototypes? Prototypes के संदर्भ में instance methods और static methods में क्या अंतर है?

Answer

Type	Defined on	Called on	Accesses instance data?
Instance method	Constructor.prototype	Individual instances	Yes, via 'this'
Static method	The constructor/class itself	The class directly, not instances	No direct instance access

function Circle(radius) {
    this.radius = radius;
}

// Instance method - on the prototype, shared by all instances
Circle.prototype.getArea = function() {
    return Math.PI * this.radius ** 2; // uses instance's own 'radius'
};

// Static method - directly on the constructor function
Circle.compare = function(circle1, circle2) {
    return circle1.getArea() - circle2.getArea();
};

const c1 = new Circle(5);
const c2 = new Circle(3);

console.log(c1.getArea()); // 78.53... - instance method
console.log(Circle.compare(c1, c2)); // static method, called on Circle directly
// console.log(c1.compare); // undefined - static methods NOT accessible on instances

// ES6 class equivalent
class CircleES6 {
    constructor(radius) {
        this.radius = radius;
    }
    getArea() { // instance method - added to CircleES6.prototype
        return Math.PI * this.radius ** 2;
    }
    static compare(c1, c2) { // static method - added directly to CircleES6
        return c1.getArea() - c2.getArea();
    }
    static fromDiameter(diameter) { // common static use: factory methods
        return new CircleES6(diameter / 2);
    }
}

const circle = CircleES6.fromDiameter(10);
console.log(circle.radius); // 5

// Verifying where each method lives
console.log(CircleES6.prototype.hasOwnProperty('getArea')); // true
console.log(CircleES6.hasOwnProperty('compare'));            // true

Type	कहाँ defined	कहाँ call होता है	Instance data access?
Instance method	Constructor.prototype	Individual instances	हाँ, 'this' से
Static method	खुद constructor/class	Class पर सीधे	नहीं

function Circle(radius) {
    this.radius = radius;
}

// Instance method - prototype पर
Circle.prototype.getArea = function() {
    return Math.PI * this.radius ** 2;
};

// Static method - constructor पर सीधे
Circle.compare = function(circle1, circle2) {
    return circle1.getArea() - circle2.getArea();
};

const c1 = new Circle(5);
const c2 = new Circle(3);

console.log(c1.getArea()); // instance method
console.log(Circle.compare(c1, c2)); // static method

// ES6 class equivalent
class CircleES6 {
    constructor(radius) {
        this.radius = radius;
    }
    getArea() {
        return Math.PI * this.radius ** 2;
    }
    static compare(c1, c2) {
        return c1.getArea() - c2.getArea();
    }
    static fromDiameter(diameter) {
        return new CircleES6(diameter / 2);
    }
}

const circle = CircleES6.fromDiameter(10);
console.log(circle.radius); // 5

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