Developers must write clean and efficient JavaScript code. This is because the code will at some point be accessed by other developers, and you will want your code to be able to be read and improved upon by said developers. Thus, your code needs to be as clean and as efficient as possible. Following best practices as a developer will help improve code readability, maintainability, and performance. When your code is read by another developer, it is easily understood, and it is also easily maintained because the developer doesn't struggle to find out what the code does.

Some of the best practices every developer can implement to write clean and efficient JavaScript code as a developer includes:

1. Use meaningful variable names: Use descriptive and meaningful names for your functions, classes, and variables. This helps other developers easily understand what the code does. Avoid using vague names as much as possible, as this could easily confuse other developers, and yourself.

    function sumOfTwoNumbers(x,y){
    }
   

   The code above is a very easy and straightforward way to name a function that takes two numbers and adds them together. It is free of ambiguity and vagueness.

2. Write modular code: Another way to write clean code, is to write modular code. This simply means breaking your code up into smaller pieces that all work together to perform a task. This reduces the load on a function and increases performance on the website.

    function createAccount() {
    // code goes here
    validateInfo()
    processPayment()
    calculateRating()
    }
   
    function validateInfo(){
    //code goes here
    }
   
    function processPayment(){
    // code goes here
    }
   
    function calculateRating(){
    // code goes here
    }
   

   In the code example above, three different functions are written, and one different function then carries the functionality of all three together. If ever there is a case to debug, it can easily be done

3. Use comments: Comments in JavaScript are a very easy way to describe what your code does. It is also advised to use comments as much as you can in your code. This is because simple comments easily explain what the code does at first glance, without having to struggle for it.

    // This function takes 2 numbers and sums them together, and thereafter returns the result
    function sumOfTwoNumbers(x,y){
    }
   

   The comment is done with two slashes and the explanation follows thereafter. As seen above, the comment explains what the code does in clear simple terms.

4. Avoid global variables: Global variables reduce flexibility and modularity. Since it is a global variable, it is likely to be shared by the whole script, and as such tampering with it may cause problems in the code. It is advised to avoid global variables as much as possible. Instead, it is better to use local variables. Such times include:

   1. Inside a function: Local variables declared inside a function are only accessible within that function. This can help prevent naming conflicts with variables declared outside the function.

    function calculateArea(radius) {
      const pi = 3.14; // Local variable
      const area = pi * radius * radius;
      return area;
    }

1. In a block of code: Local variables declared inside a block of code (such as an if statement or a for loop) are only accessible within that block. This can help prevent naming conflicts and make the code more readable.

    let x = 10;
    if (x > 5) {
      const message = "x is greater than 5"; // Local variable
      console.log(message);
    }

1. As function parameters: Function parameters act as local variables inside the function. They are only accessible within the function and do not affect variables with the same name outside the function.

    function greet(name) {
      const message = `Hello, ${name}!`; // Local variable
      console.log(message);
    }

    const name = "Alice";
    greet(name);

By using local variables in JavaScript, you can help ensure that your code is easier to read, maintain, and debug.

1. Use strict mode: Strict mode in JavaScript is a way to opt-in to a restricted variant of JavaScript, thereby implicitly opting out of "sloppy mode". Strict mode does not only apply to functions, but to the whole script, especially when declared at the top of the script, where it is usually done. It helps in correcting silent errors in JavaScript by causing errors to be thrown, and also it fixes mistakes that make it difficult for JavaScript engines to perform optimizations.

    // Whole-script strict mode syntax
    "use strict";
    const v = "Hi! I'm a strict mode script!";
   

   This is the typical way of declaring strict mode in JavaScript.

2. Use a Linter: a linter is a tool that analyzes source code in a particular programming language and flags potential problems like syntax errors, deviations from a prescribed coding style or using constructs known to be unsafe. It helps developers when they make mistakes, points them to it, and helps them know when the problem has been rectified. A very popular JavaScript linter is ESLint. It is a great tool that helps in writing clean code.

3. Keep it simple: Keeping code simple is one of the greatest hacks to writing clean JavaScript code. Not only does it improve readability, but it also helps in maintainability and performance.

These are some of the easiest ways to write clean and efficient JavaScript code. Not only does it help you stand out as a developer, but it also helps others understand your code, what it does, and how to build upon it. The benefits cannot be overemphasised and I encourage every developer to start to write clean and efficient JavaScript code, no matter the situation.