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JavaScript Examples


What can JavaScript do?

JavaScript can change HTML content
JavaScript can change HTML attributes
JavaScript can change CSS style
JavaScript can validate input


JavaScript Output

Writing into an window alert box
Writing into the HTML output
Writing into an HTML element
Writing into the browser console

Output explained


Where to Insert JavaScript

JavaScript in <head>
JavaScript in <body>
JavaScript in an external file

Placement explained


JavaScript Syntax

JavaScript statements
JavaScript numbers
JavaScript strings
JavaScript expressions
JavaScript keywords
JavaScript variables
JavaScript assignment
JavaScript operators
JavaScript comments
JavaScript is case sensitive

Syntax explained


JavaScript Statements

JavaScript statements are commands to the browser
JavaScript code is a sequence of statements
JavaScript statements are separated with semicolon
Multiple statement on one line is allowed
JavaScript statements can be grouped together in code blocks
You can break a code line after an operator or a comma.

Statements explained


JavaScript Comments

Single line comments
Single line comments at the end of a line
Multiple lines comments
Single line comment to prevent execution
Multiple lines comment to prevent execution

Comments explained


JavaScript Variables

JavaScript variables
JavaScript variables as algebra
JavaScript numbers and strings
JavaScript var keyword.
Declaring many variables in one statement
Declaring many variables multiline
A variable without a value returns the value undefined
Re-declaring a variable will not destroy the value
Adding JavaScript numbers
Adding JavaScript strings
Adding strings and numbers

Variables explained


JavaScript Arithmetic

The addition (+) operator
The subtraction (-) operator
The multiplication (*) operator
The division (/) operator
The modulus (%) operator
The increment (++) operator
The decrement (--) operator

Arithmetic explained


JavaScript Assignment

The = assignment operator
The += assignment operator
The -= assignment operator
The *= assignment operator
The /= assignment operator
The %= assignment operator

Assignment explained


JavaScript String Concatenation

Adding two strings together using the concatenating (+) operator
Adding two strings together with a space in the first string
Adding two strings together with a space in between
Adding two strings together using using the += operator
Adding strings and numbers

Concatenation explained


JavaScript Data Types

Declare (create) strings
Declare (create) numbers
Declare (create) an array
Declare (create) an object
Use typeof to find the type of variables
An undefined variable
An empty variable

Data types explained


JavaScript Objects

Create a JavaScript variable
Create a JavaScript object
Create a person object (single line)
Create a person object (multiple lines)
Access object properties using .property
Access object properties using [property]
Access a function property as a method
Access a function property as a property

Objects explained


JavaScript Functions

A simple function
A function with an argument
A function with an argument 2
A function that returns a value
A function that converts Fahrenheit to Celsius
A function call without ()

Functions explained


JavaScript Events

An onclick event changes an HTML element
An onclick event changes its own element
An onclick event calls a function

Events explained


JavaScript Strings

Strings can be written with single or double qoutes.
Show some string examples
Backslash before quotes accepts quotes as quotes.
Find the length of a string
You can break text string with a backslash.
You cannot break code with a backslash.
Find the position of the first occurrence of a text in a string - indexOf()
Search for a text in a string and return the text if found - match()
Replace characters in a string - replace()
Convert string to upper case - toUpperCase()
Convert string to lower case - toLowerCase()
Split a string into an array - split()

Strings explained


JavaScript Numbers

Number are considered accurate only up to 15 digits
Floating point arithmetic is not always 100% accurate
But it helps to multiply and divide by 10
Constants, preceded by 0x, are interpreted as hexadecimal
The toString() method can output numbers as hex, octal, and binary
JavaScript will generate Infinity if you calculate a too large number
Division by zero generates Infinity
A number divided by a string is not a number

Numbers explained


JavaScript Maths

Use Math.random() to return a random number between 0 and 1
Use Math.round() to round a number
Use Math.ceil() to round a number (up)
Use Math.floor() to round a number (down)
Use Math.floor() and random() to return a random integer
Use Math.max() to return the number with the highest value
Use Math.min() to return the number with the lowest value
Convert Celsius to Fahrenheit

Maths explained


JavaScript Dates

Use Date() to display today's date and time
Use getFullYear() display the year
Use getTime() to calculate the number of milliseconds since 1970
Use setFullYear() to set a specific date
Use toUTCString() to convert today's date (according to UTC) to a string
Use getDay() to display the weekday as a number
Use getDay() and an array to display the weekday as a name
Display a clock

Dates explained


JavaScript Arrays

Create an array
Join two arrays - concat()
Join three arrays - concat()
Join all elements of an array into a string - join()
Remove the last element of an array - pop()
Add new elements to the end of an array - push()
Reverse the order of the elements in an array - reverse()
Remove the first element of an array - shift()
Select elements from an array - slice()
Sort an array (alphabetically and ascending) - sort()
Sort numbers (numerically and ascending) - sort()
Sort numbers (numerically and descending) - sort()
Add an element to position 2 in an array - splice()
Convert an array to a string - toString()
Add new elements to the beginning of an array - unshift()

Arrays explained


JavaScript Type Conversion

Display the typeof all variable types
Display the constructor of all variable types
Convert a number to a string using String()
Convert a number to a string using toString()
Find out if a variable is an array
Find out if a variable is an date

Data Conversion Explained


JavaScript Booleans

Display the value of Boolean(10 > 9)
Display the value of 10 > 9
Everything with a real value is true
The Boolean value of zero is false
The Boolean value of minus zero is false
The Boolean value of an empty string is false
The Boolean value of undefined is false
The Boolean value of null is false
The Boolean value of false is false
The Boolean value of NaN is false

Booleans explained


JavaScript Comparisons

Assign 5 to x, and display the value of (x == 8)
Assign 5 to x, and display the value of (x == 5)
Assign 5 to x, and display the value of (x === 5)
Assign 5 to x, and display the value of (x === "5")
Assign 5 to x, and display the value of (x != 8)
Assign 5 to x, and display the value of (x !== 5)
Assign 5 to x, and display the value of (x !== "5")
Assign 5 to x, and display the value of (x > 8)
Assign 5 to x, and display the value of (x < 8)
Assign 5 to x, and display the value of (x >= 8)
Assign 5 to x, and display the value of (x <= 8)

Comparisons explained


JavaScript Conditionals

The if statement
The else statement
The else if statement
Random link
Switch statement

Conditionals explained


JavaScript Loops

For loop
Looping through HTML headers
While loop
Do While loop
Break a loop
Break and continue a loop
Use a for...in statement to loop through the elements of an object

Loops explained


JavaScript Error Handling

The try...catch statement
The try...catch statement with a confirm box
The onerror event

Errors explained


JavaScript Regular Expressions

Search for an expression in a string
Search for an expression and replace it

Regular Expressions Explained


JavaScript Objects

Creating a JavaScript variable
Creating a JavaScript object
Creating a JavaScript object (single line)
Creating a JavaScript object (multiple lines)
Creating a JavaScript object using new
Creating JavaScript objects using a constructor
Creating built-in JavaScript objects
The best way to create JavaScript variables
JavaScript objects are mutable

Objects explained


JavaScript Object Properties

Accessing properties using .property
Accessing properties using [property]
Accessing properties using for in
Adding new properties to existing objects
Deleting properties from objects

Object Properties explained



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