What Are JavaScript Statements?

JavaScript statements are the building blocks of JavaScript code. They are instructions that tell the browser what to do. Each statement performs a specific action, such as assigning a value, performing a calculation or executing a function.

JavaScript code is executed line by line and statements must follow proper syntax to avoid errors.

Basic Structure of JavaScript Statements

1. Code and Syntax: Each JavaScript statement typically ends with a semicolon (;).
2. Whitespace: JavaScript ignores extra spaces, so statements can span multiple lines.
3. Case Sensitivity: JavaScript is case-sensitive, so always use correct casing for variable and function names.

Examples of JavaScript Statements

Here are some common types of JavaScript statements with examples:

1. Variable Declaration Statement

Variables are used to store data.

let name = "John";   // Declares a variable and assigns a value
const age = 25;      // Declares a constant variable
var city = "London"; // Declares a variable (older syntax)

2. Expression Statements

These are statements that assign or calculate a value.

let sum = 10 + 20;   // Adds two numbers and stores the result
let fullName = name + " Doe"; // Combines strings

3. Conditional Statements

Conditional statements allow you to make decisions based on certain conditions.

Example: if…else

if (age >= 18) {
  console.log("You are an adult.");
} else {
  console.log("You are not an adult.");
}

4. Loop Statements

Loop statements execute a block of code multiple times.

Example: for Loop

for (let i = 1; i <= 5; i++) {
  console.log("Iteration " + i);
}

5. Function Declaration Statement

Functions are reusable blocks of code that perform a task.

function greet() {
  console.log("Hello, welcome to JavaScript!");
}
greet(); // Calls the function

6. Return Statement

The return statement is used in functions to send a value back to the caller.

function addNumbers(a, b) {
  return a + b;
}
let result = addNumbers(5, 10); // result is 15

7. Block Statement

Block statements group multiple statements together, enclosed in curly braces {}.

{
  let x = 10;
  let y = 20;
  console.log(x + y); // Outputs 30
}

Important Notes About JavaScript Statements

1. Semicolons Are Optional
   JavaScript does not require semicolons, but adding them helps prevent errors and makes your code more readable.
2. Statements vs. Expressions
   • A statement performs an action, such as declaring a variable or creating a loop.
   • An expression produces a value, such as 5 + 10.

Best Practices for Writing JavaScript Statements

Use Clear and Descriptive Variable Names
Instead of using short or unclear names, choose names that make the purpose of the variable obvious.

let x = 10;          // Not clear
let itemCount = 10;  // Clear and descriptive

Break Long Statements for Readability
Use line breaks and indentation for better readability.

let message = 
    "This is a long statement " +
    "that spans multiple lines.";

Keep It Simple and Organized
Write statements that are easy to understand and maintain.

Real-Life Example: Using Multiple Statements Together

Here is an example that combines variable declarations, conditionals, and loops.

let students = ["John", "Jane", "Alex", "Emma"]; // Array of students

for (let i = 0; i < students.length; i++) {
  if (students[i].startsWith("J")) {
    console.log(students[i] + " starts with J.");
  } else {
    console.log(students[i] + " does not start with J.");
  }
}

Output:

John starts with J.
Jane starts with J.
Alex does not start with J.
Emma does not start with J.