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this_demo.cjs
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this_demo.cjs
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// Demonstration of 'this' keyword and 'new' operator
console.log("=== Constructor Functions with 'new' and 'this' ===\n");
// Basic constructor function
function Person(name, age) {
this.name = name;
this.age = age;
this.greet = function() {
return "Hello, my name is " + this.name + " and I am " + this.age + " years old.";
};
}
// Create instances using 'new'
console.log("Creating person1 with new Person('Alice', 30)");
let person1 = new Person("Alice", 30);
console.log("person1.name:", person1.name);
console.log("person1.age:", person1.age);
console.log("person1.greet():", person1.greet());
console.log();
console.log("Creating person2 with new Person('Bob', 25)");
let person2 = new Person("Bob", 25);
console.log("person2.name:", person2.name);
console.log("person2.age:", person2.age);
console.log("person2.greet():", person2.greet());
console.log();
// Each instance has its own 'this' context
console.log("=== Independent 'this' contexts ===");
console.log("person1.name:", person1.name);
console.log("person2.name:", person2.name);
console.log("They are different instances with independent 'this' values");
console.log();
// Constructor with methods that use 'this'
function Counter(start) {
this.value = start;
this.increment = function() {
this.value = this.value + 1;
return this.value;
};
this.decrement = function() {
this.value = this.value - 1;
return this.value;
};
this.getValue = function() {
return this.value;
};
}
console.log("=== Counter Example ===");
let counter = new Counter(10);
console.log("Initial value:", counter.getValue());
console.log("After increment:", counter.increment());
console.log("After increment:", counter.increment());
console.log("After decrement:", counter.decrement());
console.log("Final value:", counter.getValue());
console.log();
// Multiple counters with independent state
console.log("=== Multiple Independent Counters ===");
let counter1 = new Counter(0);
let counter2 = new Counter(100);
console.log("counter1 initial:", counter1.getValue());
console.log("counter2 initial:", counter2.getValue());
counter1.increment();
counter1.increment();
counter2.decrement();
console.log("counter1 after 2 increments:", counter1.getValue());
console.log("counter2 after 1 decrement:", counter2.getValue());
console.log();
// Constructor with computed properties
function Rectangle(width, height) {
this.width = width;
this.height = height;
this.area = function() {
return this.width * this.height;
};
this.perimeter = function() {
return 2 * (this.width + this.height);
};
}
console.log("=== Rectangle Example ===");
let rect1 = new Rectangle(5, 10);
console.log("Rectangle 5x10:");
console.log(" Width:", rect1.width);
console.log(" Height:", rect1.height);
console.log(" Area:", rect1.area());
console.log(" Perimeter:", rect1.perimeter());
console.log();
let rect2 = new Rectangle(3, 7);
console.log("Rectangle 3x7:");
console.log(" Width:", rect2.width);
console.log(" Height:", rect2.height);
console.log(" Area:", rect2.area());
console.log(" Perimeter:", rect2.perimeter());
console.log();
// 'this' refers to the object being constructed
function Car(make, model, year) {
this.make = make;
this.model = model;
this.year = year;
this.displayInfo = function() {
return this.year + " " + this.make + " " + this.model;
};
}
console.log("=== Car Example ===");
let car1 = new Car("Toyota", "Camry", 2020);
let car2 = new Car("Honda", "Civic", 2021);
console.log("car1:", car1.displayInfo());
console.log("car2:", car2.displayInfo());
console.log();
// 'this' in nested functions
function Account(owner, balance) {
this.owner = owner;
this.balance = balance;
this.deposit = function(amount) {
this.balance = this.balance + amount;
return this.balance;
};
this.withdraw = function(amount) {
this.balance = this.balance - amount;
return this.balance;
};
this.getInfo = function() {
return this.owner + " has $" + this.balance;
};
}
console.log("=== Bank Account Example ===");
let account1 = new Account("Alice", 1000);
console.log("Initial:", account1.getInfo());
account1.deposit(500);
console.log("After deposit 500:", account1.getInfo());
account1.withdraw(200);
console.log("After withdraw 200:", account1.getInfo());
console.log();
// Multiple accounts
let account2 = new Account("Bob", 2000);
console.log("account1:", account1.getInfo());
console.log("account2:", account2.getInfo());
console.log();
console.log("=== Summary ===");
console.log("- 'new' creates a new object");
console.log("- 'this' inside constructor refers to the new object");
console.log("- Each instance has its own 'this' context");
console.log("- Methods can access and modify 'this' properties");

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