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Chapter 2. JavaScript Statements and Comments


JavaScript, a cornerstone of web development, is composed of various building blocks that define its functionality. Two fundamental aspects of JavaScript are statements and comments. Understanding these elements is crucial for writing clear, efficient, and maintainable code.

JavaScript Statements

In JavaScript, a statement is an instruction that the browser executes. These instructions can perform actions such as declaring variables, making decisions, or executing loops. Here are some key points about JavaScript statements:

Syntax: Each JavaScript statement should end with a semicolon (;). However, JavaScript does allow for automatic semicolon insertion (ASI), meaning the semicolon is optional in many cases. Despite this, it’s a good practice to use semicolons to avoid potential pitfalls

Types of Statements:

    Variable Declaration: let, const, and var are used to declare variables.

    let name = 'Alice';
    const age = 30;
    var city = 'New York';

    Control Flow: Statements like if, else, switch, for, while, and do-while control the flow of the program.

    if (age > 18) {
    } else {
    for (let i = 0; i < 5; i++) {

    Function Declaration: Defines a reusable block of code.

    function greet(name) {
        return `Hello, ${name}!`;

    Expression Statements: Evaluates expressions.

    let sum = 5 + 10;

    Return Statement: Exits a function and optionally returns a value.

    function add(a, b) {
        return a + b;

    Block Statements:

    Enclosed in curly braces {}, a block statement groups zero or more statements.

        let x = 10;
        let y = 20;
        console.log(x + y);

    JavaScript Comments

    Comments are non-executable portions of code used to describe and explain code logic. They are essential for maintaining and understanding code, especially in collaborative environments.

    Single-Line Comments: Use // to create a single-line comment.

         // This is a single-line comment
         let x = 5; // Assigning 5 to variable x

      Multi-Line Comments: Use /* */ to create a comment that spans multiple lines.

           This is a multi-line comment
           that can span multiple lines.
           let y = 10;

        Comment Best Practices:

        • Clarity: Use comments to explain the why, not the what. Code should be self-explanatory for what it does.
        • Update Regularly: Ensure comments are updated when code changes to avoid misleading information.
        • Avoid Obvious Comments: Don’t clutter the code with comments stating the obvious.

          Examples of Statements and Comments in Action

          Here’s an example that combines various JavaScript statements and comments:

          // Declare and initialize a variable
          let name = 'Alice';
          /* Function to greet a user
             Takes one argument: name */
          function greet(name) {
              // Return a greeting message
              return `Hello, ${name}!`;
          // Call the function and log the result
          console.log(greet(name)); // Output: Hello, Alice!


          JavaScript statements and comments are fundamental elements of coding in JavaScript. Statements perform actions and control the flow of the program, while comments provide explanations and context. Mastering the use of these components is essential for writing effective and maintainable JavaScript code. By following best practices and maintaining clarity in your code, you can ensure that your JavaScript programs are both functional and easy to understand.

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