to JavaScript Classes:
JavaScript is a powerful programming language that allows developers to create complex software applications, including websites and mobile apps. One of the key features of JavaScript is the ability to create classes, which serve as blueprints for objects.
In this article, we will explore the purpose and definition of a JavaScript class, the different approaches to implementing classes in ES5 and ES6, as well as the differences between classes and custom types. By the end of this article, you will have a better understanding of what classes are, how they work in JavaScript, and why they are an essential component of any developer’s toolkit.
ES5 Approach to Classes using Constructor/Prototype Pattern:
The ES5 approach to creating classes in JavaScript involves using the constructor/prototype pattern. In this pattern, we define a constructor function that creates new instances of a certain type, and then assign methods and properties to the prototype object of the constructor function.
This allows us to create objects that share common functionality, minimizing code duplication and making our code more modular and maintainable. For example, consider the following code snippet:
“`
function Person(name, age, gender) {
this.name = name;
this.age = age;
this.gender = gender;
}
Person.prototype.greet = function() {
console.log(“Hello, my name is ” + this.name + ” and I am ” + this.age + ” years old.”);
}
“`
In this example, we have defined a `Person` constructor function that takes three parameters – `name`, `age`, and `gender` – and assigns them to properties of the new object.
We have also defined a `greet` method on the prototype object of the `Person` constructor, which allows us to log a greeting for each new instance of the `Person` type. To create a new `Person` instance, we can use the `new` operator to invoke the constructor function and pass in the required parameters:
“`
var john = new Person(“John”, 30, “Male”);
john.greet(); // Output: “Hello, my name is John and I am 30 years old.”
“`
ES6 Approach to Classes using the Class Keyword:
In ES6, we have a more concise and intuitive way of defining classes using the `class` keyword.
The basic syntax for creating a class in ES6 is as follows:
“`
class Person {
constructor(name, age, gender) {
this.name = name;
this.age = age;
this.gender = gender;
}
greet() {
console.log(“Hello, my name is ” + this.name + ” and I am ” + this.age + ” years old.”);
}
}
“`
In this example, we have defined a `Person` class using the `class` keyword. Inside the class, we have defined a constructor method that takes the required parameters and assigns them to properties of the new object.
We have also defined a `greet` method, which is similar to the one we defined in the ES5 approach. To create a new `Person` instance using the ES6 approach, we can simply use the `new` operator and pass in the required parameters:
“`
let john = new Person(“John”, 30, “Male”);
john.greet(); // Output: “Hello, my name is John and I am 30 years old.”
“`
Differences between Classes and Custom Types:
While classes in JavaScript are similar in some ways to custom types, there are several important differences that make them distinct.
Let’s explore some of these differences in more detail:
Non-Hoisting of Class Declarations:
One key difference between classes and custom types is that class declarations are not hoisted, whereas function declarations are. In other words, we cannot use a class before we declare it, whereas we can use a function before we declare it.
For example, consider the following code snippet:
“`
var p = new Person(“John”, 30, “Male”); // ReferenceError: Person is not defined
class Person {
constructor(name, age, gender) {
this.name = name;
this.age = age;
this.gender = gender;
}
}
“`
In this example, we are trying to create a new `Person` instance before we have defined the `Person` class. Because class declarations are not hoisted, we will receive a `ReferenceError` when we try to call the `Person` constructor.
Strict Mode in Classes:
Another difference between classes and custom types is that all code inside a class declaration is automatically in strict mode, whereas code outside of a class declaration is not. This means that certain behaviors, such as using undeclared variables or using the `with` keyword, are disallowed inside a class.
Non-Enumerable Class Methods:
By default, methods defined on the prototype of a class are non-enumerable, meaning they will not show up in a `for…in` loop. This is different from regular object properties, which are enumerable by default.
To make a class method enumerable, we can use the `Object.defineProperty()` method and set the `enumerable` property to true. Error when Calling Class Constructor without New Operator:
Finally, when calling a class constructor, we must use the `new` operator to create a new instance of the class.
If we forget to use the `new` operator, we will receive an error, as the constructor has not been called in a valid context. For example, consider the following code snippet:
“`
var john = Person(“John”, 30, “Male”); // Error: Class constructor Person cannot be invoked without ‘new’
“`
In this example, we have forgotten to use the `new` operator when calling the `Person` constructor, resulting in an error.
Conclusion:
In conclusion, classes are an essential component of any developer’s toolkit, allowing us to create blueprints for objects with shared functionality. We have explored the differences between the ES5 and ES6 approaches to creating classes, as well as the differences between classes and custom types.
By understanding these differences and how they impact our code, we can write more efficient and effective software applications. In conclusion, JavaScript classes allow developers to create blueprints for objects that share the same functionality and minimize code duplication.
ES5 and ES6 approaches to classes provide different ways to define classes, with the latter offering a more concise and intuitive way to create them. Additionally, the primary differences between classes and custom types lie in the non-hoisting of class declarations, strict mode, non-enumerable class methods, and the requirement to use the new operator when calling a class constructor.
By understanding these differences, developers can write more efficient and effective software applications. The importance of understanding these differences cannot be overstated, as classes are an essential component of any developer’s toolkit.