JavaScript Statements
Building blocks of JavaScript programs
📝 What are JavaScript Statements?
JavaScript statements are instructions that tell the browser what to do. They are executed one by one, from top to bottom. Each statement usually ends with a semicolon (;).
// This is a simple JavaScript statement
console.log("Hello, World!");
let message = "Welcome to JavaScript!";
Console Output:
Hello, World!
Types of JavaScript Statements
Variable Statements
Declare and assign variables
let name = "John";
const age = 25;
var city = "New York";Control Statements
Control program flow
if (age >= 18) {
console.log("Adult");
}Loop Statements
Repeat code execution
for (let i = 0; i < 5; i++) {
console.log(i);
}Function Statements
Define reusable code blocks
function greet() {
return "Hello!";
}🔹 Variable Declaration Statements
Variables store data values. JavaScript has three ways to declare variables:
// let - for variables that can change
let userName = "Alice";
userName = "Bob"; // Can be changed
// const - for constants that cannot change
const PI = 3.14159;
// PI = 3.14; // This would cause an error!
// var - older way (avoid in modern JavaScript)
var oldStyle = "Not recommended";
// Using the variables
console.log("User: " + userName);
console.log("PI value: " + PI);Console Output:
User: Bob
PI value: 3.14159
🔹 Assignment Statements
Assignment statements give values to variables:
// Basic assignment
let score = 100;
// Multiple assignments
let x = 5, y = 10, z = 15;
// Assignment with operations
let total = x + y + z;
let doubled = score * 2;
// String assignment
let firstName = "John";
let lastName = "Doe";
let fullName = firstName + " " + lastName;
console.log("Total: " + total);
console.log("Full Name: " + fullName);Console Output:
Total: 30
Full Name: John Doe
🔹 Conditional Statements
Make decisions in your code with if, else if, and else:
let temperature = 25;
// Simple if statement
if (temperature > 30) {
console.log("It's hot!");
}
// if-else statement
if (temperature < 0) {
console.log("It's freezing!");
} else {
console.log("Temperature is above freezing");
}
// if-else if-else statement
let weather;
if (temperature > 30) {
weather = "Hot";
} else if (temperature > 20) {
weather = "Warm";
} else if (temperature > 10) {
weather = "Cool";
} else {
weather = "Cold";
}
console.log("Weather: " + weather);Console Output:
Temperature is above freezing
Weather: Warm
🔹 Loop Statements
Repeat code multiple times with different types of loops:
🔸 For Loop
// Count from 1 to 5
for (let i = 1; i <= 5; i++) {
console.log("Count: " + i);
}
// Loop through an array
let fruits = ["apple", "banana", "orange"];
for (let i = 0; i < fruits.length; i++) {
console.log("Fruit: " + fruits[i]);
}🔸 While Loop
// Count down from 5
let countdown = 5;
while (countdown > 0) {
console.log("Countdown: " + countdown);
countdown--;
}
console.log("Blast off!");Console Output:
Count: 1
Count: 2
Count: 3
Count: 4
Count: 5
Fruit: apple
Fruit: banana
Fruit: orange
Countdown: 5
Countdown: 4
Countdown: 3
Countdown: 2
Countdown: 1
Blast off!
🔹 Function Statements
Create reusable blocks of code with functions:
// Function declaration
function sayHello(name) {
return "Hello, " + name + "!";
}
// Function with multiple parameters
function addNumbers(a, b) {
let sum = a + b;
return sum;
}
// Function without parameters
function getCurrentTime() {
return new Date().toLocaleTimeString();
}
// Using the functions
let greeting = sayHello("Alice");
let result = addNumbers(10, 20);
let time = getCurrentTime();
console.log(greeting);
console.log("Sum: " + result);
console.log("Current time: " + time);Console Output:
Hello, Alice!
Sum: 30
Current time: 2:30:45 PM
🔹 Statement Syntax Rules
Important rules for writing JavaScript statements:
✅ Good Practices:
- Semicolons: End statements with semicolons (;)
- Indentation: Use consistent indentation for readability
- Line breaks: One statement per line
- Comments: Use // for single-line comments
// Good: Clear and readable
let userName = "John";
let userAge = 25;
if (userAge >= 18) {
console.log(userName + " is an adult");
} else {
console.log(userName + " is a minor");
}
// Avoid: Multiple statements on one line
let a = 1; let b = 2; let c = 3; // Hard to read