Data Types

There are several different data types in JavaScript. The most common ones are covered in this video.

For reference, here are the data types that we covered in the video:

• String: A string is a sequence of characters. Strings are used to represent text. Strings are declared using double quotes (") or single quotes (').

• Number: A number is a numeric value. Numbers can be integers (whole numbers) or floating-point numbers (numbers with a decimal point). Numbers are declared without quotes.

• Boolean: A boolean is a value that is either true or false. Booleans are used to represent the truth value of an expression. Booleans are declared without quotes.

• Null: Null is a special value that represents "nothing". Null is declared without quotes.

• Undefined: Undefined is a special value that represents a variable that has not been assigned a value. Undefined is declared without quotes.

• Object: An object is a collection of key-value pairs. Objects are declared using curly braces ({}).

• Array: An array is a collection of values. Arrays are declared using square brackets ([]).

• Function: A function is a block of code that can be called by name. Functions are declared using the function keyword.

Comments

Comments in JavaScript are similar to comments in C#. Single-line comments start with // and multi-line comments start with /* and end with */. Here is an example:

// This is a single-line comment

/*
This is a multi-line comment.
See how it spans multiple lines?
So spany lines. Much comment. Very multi-line. Wow. - Doge
*/

Assignment Operators

Assignment operators are used to assign values to variables. The most common assignment operator is =. Here is an example:

let x = 5
console.log(x) // 5

Arithmetic Operators

Arithmetic operators are used to perform arithmetic operations on numbers. The most common arithmetic operators are +, -, *, /, and %. Here is an example:

const a = 10
const b = 3
const c = a + b // 13
const d = a - b // 7
const e = a * b // 30
const f = a / b // 3.333333
const g = a % b // 1

Comparison Operators

Comparison operators are used to compare two values. The most common comparison operators are ==, !=, ===, !==, >, <, >=, and <=. Here is an example:

let x = 5
let y = 10
console.log(x == y) // false
console.log(x != y) // true
console.log(x === y) // false
console.log(x !== y) // true
console.log(x > y) // false
console.log(x < y) // true
console.log(x >= y) // false
console.log(x <= y) // true

Logical Operators

Logical operators are used to combine multiple conditions. The most common logical operators are && (and), || (or), and ! (not). Let's take a look:

let x = 5
let y = 10
console.log(x > 0 && y > 0) // true
console.log(x > 0 || y > 0) // true
console.log(!(x > 0)) // false

Increment and Decrement Operators

Increment and decrement operators are used to modify the value of a variable. They work just like you are used to from C#. Let's take a look:

let x = 5
x++
console.log(x) // 6
x--
console.log(x) // 5
x += 10
console.log(x) // 15
x -= 10
console.log(x) // 5

Ternary Operator

The ternary operator is used to assign a value to a variable based on a condition. It is similar to an if statement. Here is an example:

let x = 5
let y = x > 0 ? "positive" : "negative"
console.log(y) // "positive"

Hint

const p = document.querySelector('p')
p.textContent = 'Hello world'

Solution

const p = document.querySelector('p')

setTimeout(() => {
    p.textContent = '3 seconds elapsed'
}, 3000)