JavaScript Examples
What can JavaScript do?
JavaScript can change HTML content
JavaScript can change HTML attributes
JavaScript can change CSS style
JavaScript can hide HTML elements
JavaScript can show hidden HTML elements
Examples Explained
Where to Insert JavaScript
JavaScript in <head>
JavaScript in <body>
JavaScript in an external file
JavaScript in an external url
JavaScript in an external folder
Where to Explained
JavaScript Output
Writing into the HTML output
Writing into an HTML element
Writing into an window alert box
Writing into the browser console
Output Explained
JavaScript Syntax
JavaScript statements
JavaScript numbers
JavaScript strings
JavaScript variables
JavaScript operators
JavaScript assignment
JavaScript expressions (using constants)
JavaScript expressions (using strings)
JavaScript expressions (using variables)
JavaScript keywords
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
Find the type of a variable
Adding two numbers and a string
Adding a string and two numbers
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 quotes.
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
Numbers can be written with or without decimals
Extra large or extra small numbers can be written with exponent notation
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
Adding two numbers results in a new number
Adding two numeric strings results in a concatenated string
Adding a number and a numeric string also results in a concatenated string
Adding a numeric string and a number also results in a concatenated string
Common mistake when adding strings and numbers 1
Common mistake when adding strings and numbers 2
JavaScript will try to convert strings to numbers when dividing
JavaScript will try to convert strings to numbers when multiplying
JavaScript will try to convert strings to numbers when subtracting
JavaScript will NOT convert strings to numbers when adding
A number divided by a string is NaN (Not a Number)
A number divided by a numeric string is a number
The global JavaScript function isNaN() returns if a value is a number
Using NaN in a mathematical operation will always return NaN
Using NaN in a mathematical string operation will concatenate NaN
NaN (Not a Number) is a number (Yes! typeof NaN returns number)
Infinity is returned if you calculate a number outside the largest possible number
Division by zero also generates Infinity
Infinity is a number (typeof Infinity returns number)
Constants, preceded by 0x, are interpreted as hexadecimal
The toString() method can output numbers as hex, octal, and binary
Numbers can be objects
Numbers and objects cannot be safely compared
Objects and objects cannot be safely compared
Numbers Explained
JavaScript Number Methods
The toString() method converts a number to a string
The valueOf() method returns a number as a number
The toExponential() returns a number with exponential notation
The toFixed() method rounds a number to a number of digits
The toPrecision() method a number written with a specified length
The global method Number() converts variables to numbers
The global method Number() can even convert dates to numbers
The global method parseInt() converts strings to numbers
The global method parseFloat() converts strings to numbers
MAX_VALUE returns the largest possible number in JavaScript
MIN_VALUE returns the smallest possible number in JavaScript
POSITIVE_INFINITY represents infinity
POSITIVE_INFINITY is returned on overflow
NEGATIVE_INFINITY represents negative infinity
NEGATIVE_INFINITY is returned on overflow
NaN Represents "Not-a-Number"
Arithmetic performed on a string will result in NaN
Using a Number property on a variable will return undefined
Numbers Methods Explained
JavaScript Maths
Math.PI returns the value of PI
Math.round(x) returns the rounded value of x
Math.pow(x, y) returns the value of x to the power of y
Math.sqrt(x) returns the square root of x
Math.abs(x) returns the absolute (positive) value of x
Math.ceil(x) returns the value of x rounded up
Math.floor(x) returns the value of x rounded down
Math.sin(x) returns the sin of the angle x (given in radians)
Math.cos(x) returns the cosin of the angle x (given in radians)
Math.max() return the number with the highest value from a list of arguments
Math.min() to return the number with the lowest value from a list of arguments
Converting Celsius to Fahrenheit
Maths Explained
JavaScript Random
Math.random() returns a random number between 0 (included) and 1 (excluded)
How to return a random integer between 0 and 9 (both included)
How to return a random integer between 0 and 10 (both included)
How to return a random integer between 0 and 99 (both included)
How to return a random integer between 0 and 100 (both included)
How to return a random integer between 1 and 10 (both included)
How to return a random integer between 1 and 100 (both included)
How to return a random integer between x (included) and y (excluded)
How to return a random integer between x and y (both included)
Random 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 I
Create an array II
Access an array element
Change an array element
Access a full array
Find the length of an array
Loop through an array
Add an element to an array
Add undefined "holes" to an array
How to
recognize an array I
How to
recognize an array II
Arrays Explained
JavaScript Array Methods
Add an element to an array
Remove the last element of an array - pop()
Join all elements of an array into a string - join()
Join two arrays - concat()
Join three arrays - concat()
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()
Remove the first element of an array - shift()
Select elements from an array - slice()
Array Methods Explained
JavaScript Array Sort
Sort an array in ascending order
Sort an array in descending order
Sort an array of numbers ascending
Sort an array of numbers descending
Sort numbers (alphabetically or numerically)
Sort array numbers in random order
Find the lowest number in an array
Find the highest number in an array
Find the lowest number in an array using Math.min()
Find the highest number in an array using Math.max()
Using a "homemade" myArrayMin method
Using a "homemade" myArrayMax method
Sort objects by numeric properties
Sort objects by string properties
Array Sort Explained
JavaScript Array Iteration
Array.forEach()
Array.map()
Array.filter()
Array.reduce()
Array.reduceRight()
Array.every()
Array.some()
Array.indexOf()
Array.lastIndexOf()
Array.find()
Array.findIndex()
Array Iteration 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 a date
Type 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 an Array
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
JSON Objects
Accessing properties using .property
Accessing properties using [property]
Looping through properties
Looping through property values
Access nested JSON objects
Modify values using the dot notation
Modify values using the bracket notation
Delete object properties
JSON Object Properties Explained
JSON Arrays
Accessing array values
Looping through an array using for-in
Looping through an array using for
Access nested JSON arrays
Modify array values
Delete array items
JSON Arrays Explained
JSON Parse
Use JSON parse
Using JSON parse in an AJAX example
Using JSON parse on an array
Parsing dates
Parsing dates using the reviver function
Parsing functions
JSON Parse Explained
JSON Stringify
Use JSON stringify
Using JSON stringify on an array
Stringify dates
Stringify functions
Stringify functions using the toString() method
JSON Stringify Explained
JSON PHP
Get JSON from a php file
Get JSON array from php
Get JSON from a database
Loop through the result from a database
Send JSON using POST method
JSON PHP Explained
JSON HTML
Make an HTML table based on JSON data
Make a dynamic HTML Table
Make an HTML drop down list based on JSON data
JSON HTML Explained
JSON JSONP
Simple JSONP example
Create a dynamic script tag
JSONP example with dynamic result
JSONP example with a callback function
JSON JSONP Explained
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Reference: https://www.w3schools.com/js/js_examples.asp