Mastering JavaScript Classes with 15 Steps to Best Practices

JavaScript, with its evolving nature, has incorporated class-based object-oriented features, bridging the gap between the prototypal inheritance it was built on and the more familiar class systems of other languages. Yet, this blend can sometimes be a trap for developers. Let’s explore some common mistakes made while using classes in JavaScript.

1. Using Undeclared Instance Variables

Incorrect Usage:

class User {
    constructor(name) {
        this.name = name;
    }
    
    setAge(age) {
        this.age = age; // This was never declared in the constructor
    }
}

Correct Usage:

class User {
    constructor(name, age) {
        this.name = name;
        this.age = age;
    }
    
    setAge(age) {
        this.age = age;
    }
}

Explanation: Always declare instance variables in the constructor. This not only provides clarity about the data each instance will carry but also ensures uniformity across instances.

2. Misusing Static Methods

Incorrect Usage:

class Calculator {
    constructor() {}
    
     static add(x, y) {
        return x + y;
    }
}

const calc = new Calculator();
calc.add(2, 3);  // Error: calc.add is not a function