**Course Title:** Mastering TypeScript: From Basics to Advanced Applications **Section Title:** Classes and Object-Oriented Programming **Topic:** Access modifiers: public, private, and protected ### Introduction to Access Modifiers In object-oriented programming, access modifiers play a crucial role in controlling access to the properties and methods of a class. In TypeScript, you can use access modifiers to restrict or allow access to class members from outside the class. In this topic, we will explore the three types of access modifiers in TypeScript: public, private, and protected. ### Public Access Modifier By default, all class members in TypeScript are public. This means that they can be accessed from anywhere in the code. When a class member is declared as public, it can be accessed without any restrictions. ```typescript class Person { public name: string; constructor(name: string) { this.name = name; } } let person = new Person('John Doe'); console.log(person.name); // Outputs: John Doe ``` In the above example, the `name` property is public and can be accessed directly using the dot notation. ### Private Access Modifier When a class member is declared as private, it can only be accessed within the same class. Trying to access a private member from outside the class will result in a compiler error. ```typescript class Person { private name: string; constructor(name: string) { this.name = name; } public getName(): string { return this.name; } } let person = new Person('John Doe'); console.log(person.getName()); // Outputs: John Doe console.log(person.name); // Compiler error: Property 'name' is private and only accessible within class 'Person' ``` In the above example, the `name` property is private and can only be accessed within the `Person` class. The `getName()` method is used to access the private `name` property. ### Protected Access Modifier When a class member is declared as protected, it can be accessed within the same class and by any class that inherits from it. Trying to access a protected member from outside the class or a non-inheriting class will result in a compiler error. ```typescript class Person { protected name: string; constructor(name: string) { this.name = name; } } class Employee extends Person { constructor(name: string, public department: string) { super(name); } public getEmployeeDetails(): string { return `Name: ${this.name}, Department: ${this.department}`; } } let employee = new Employee('John Doe', 'HR'); console.log(employee.getEmployeeDetails()); // Outputs: Name: John Doe, Department: HR console.log(employee.name); // Compiler error: Property 'name' is protected and only accessible within class 'Person' and its subclasses ``` In the above example, the `name` property is protected and can be accessed within the `Person` class and by the `Employee` class that inherits from it. The `getEmployeeDetails()` method is used to access the protected `name` property. ### Best Practices and Takeaways * Use public access modifiers for class members that need to be accessed from outside the class. * Use private access modifiers for class members that should only be accessed within the same class. * Use protected access modifiers for class members that should be accessed within the same class and by inheritance. * Always use access modifiers to control access to class members, even if it's just a private class. * Use getter and setter methods to access and modify private and protected properties. ### Resources and Further Learning * [TypeScript Documentation - Access Modifiers](https://www.typescriptlang.org/docs/handbook/classes.html#accessmodifiers) * [TypeScript TypeScript Handbook - Classes](https://www.typescriptlang.org/docs/handbook/classes.html) Please leave a comment or ask for help if you have any questions or need further clarification on this topic. We will cover the topic "Static properties and methods, and abstract classes" in the next section. Remember that practice makes perfect. Try to create your own classes with different access modifiers to solidify your understanding of this concept.