Learn about data types, conditional statements, and loops in JavaScript
JavaScript is a dynamically typed language, meaning variables can hold values of any type without specifying the type explicitly.
// String: textual data
let name = "John Doe";
let message = 'Hello World!';
// Number: integer and floating point numbers
let age = 30;
let temperature = 36.6;
// Boolean: true or false
let isStudent = true;
let isLoggedIn = false;
// Undefined: variable that has not been assigned a value
let undefinedVar;
// Null: intentional absence of any object value
let emptyValue = null;
// Symbol: unique and immutable primitive value
let sym = Symbol('description');
// BigInt: integers larger than 2^53 - 1
let bigNumber = 1234567890123456789012345678901234567890n;// Object: collection of key-value pairs
let person = {
name: "Alice",
age: 25,
isStudent: true
};
// Array: ordered list of values
let colors = ["red", "green", "blue"];
let numbers = [1, 2, 3, 4, 5];
// Function: callable object
function greet(name) {
return "Hello, " + name + "!";
}
// Date: represents a specific moment in time
let today = new Date();// Type checking with typeof operator
typeof "Hello"; // "string"
typeof 42; // "number"
typeof true; // "boolean"
typeof undefined; // "undefined"
typeof null; // "object" (historical bug)
// Type conversion
let numStr = "123";
let num = Number(numStr); // Convert to number: 123
let numVal = 456;
let strVal = String(numVal); // Convert to string: "456"
let boolVal = Boolean(1); // Convert to boolean: trueConditional statements allow you to execute different code blocks based on different conditions.
let age = 18;
// Simple if statement
if (age >= 18) {
console.log("You are an adult.");
}
// if-else statement
if (age >= 18) {
console.log("You can vote.");
} else {
console.log("You are too young to vote.");
}
// if-else if-else statement
if (age < 13) {
console.log("You are a child.");
} else if (age < 18) {
console.log("You are a teenager.");
} else {
console.log("You are an adult.");
}let day = "Monday";
switch (day) {
case "Monday":
console.log("Start of the work week");
break;
case "Tuesday":
case "Wednesday":
case "Thursday":
console.log("Midweek days");
break;
case "Friday":
console.log("End of the work week");
break;
case "Saturday":
case "Sunday":
console.log("Weekend!");
break;
default:
console.log("Invalid day");
}// Syntax: condition ? expressionIfTrue : expressionIfFalse
let age = 20;
let message = age >= 18 ? "Adult" : "Minor";
console.log(message); // "Adult"
// Multiple conditions
let speed = 75;
let warning = speed > 80 ? "Too fast" : speed > 60 ? "Moderate" : "Normal";
console.log(warning); // "Moderate"Loops allow you to execute a block of code repeatedly until a certain condition is met.
// Basic for loop
for (let i = 0; i < 5; i++) {
console.log("Iteration: " + i);
}
// Looping through an array
let fruits = ["Apple", "Banana", "Cherry"];
for (let i = 0; i < fruits.length; i++) {
console.log(fruits[i]);
}
// Nested for loops
for (let i = 0; i < 3; i++) {
for (let j = 0; j < 2; j++) {
console.log(`i: ${i}, j: ${j}`);
}
}// while loop - checks condition before execution
let count = 0;
while (count < 5) {
console.log("Count: " + count);
count++;
}
// do-while loop - executes at least once
let num;
do {
num = Math.floor(Math.random() * 10);
console.log("Random number: " + num);
} while (num !== 5);// for...of loop (for iterables like arrays, strings)
let colors = ["red", "green", "blue"];
for (let color of colors) {
console.log(color);
}
let str = "Hello";
for (let char of str) {
console.log(char);
}
// for...in loop (for object properties)
let person = {
name: "John",
age: 30,
occupation: "Developer"
};
for (let key in person) {
console.log(key + ": " + person[key]);
}