In One Video

Lesson 29
Author : GOUP
Last Updated : September, 2020

JavaScript Overview

Javascript is a high-level, dynamically typed and interpreted, programming language that was created in May of 1995 by Netscape employee Brendan Eich.

The language was famously created in only 10 days and adopted the name Javascript as a marketing play, playing off the hugly popular Java programming language. Although ironically the two languages are very different.

Javascript was built with the sole purpose of making websites more responsive and dynamic. Because it’s able to respond to user interactions and access and manipulate the document object model (DOM), Javascript allows web developers to make more dynamic websites.

In 1996 the early version of Javascript was adopted into a formal language specification called ECMAScript, of which Javascript was the most well known implementation. By specifying the language formally, all browsers could support languages implementing ECMAScript. So Technically Javascript is based off the ECMAScript specification.

How JavaScript Runs

Today Javascript is a staple, used on just about every modern website. It’s become one of the three core web development technologies along-side HTML and CSS.

Because javascript is a core web development technology and most web developers know it, Javascript has been stretched beyond it’s original purpose. Now-a-day’s there are thousands of javascript frameworks and it’s even used as a server-side language.

Javascript utilizes a garbage collector and it’s syntax is loosly based on C/C++.

Choosing an IDE

Many developers choose to write Javascript using a basic text editor, generally Javascript will be written in the same enviornment as the HTML and front end technologies that it interacts with. In many cases javascript will be written directly inside of an HTML file, but can also be palced in it’s own separate Javascript file and imported into HTML.

Code

Printing

Copydocument.write("<h1>Hello World</h1>");
document.write("<hr>");
document.write("<p>This is a javascript tutorial</p>");
alert("This is an alert");
console.log("Logging to the console");

Variables and Data Types

Copy/*
Names are case-sensitive and may begin with:
     letters, $, _
After, may include
     letters, numbers, $, _
Convention says
     Start with a lowercase word, then additional words are capitalized
     ex. myFirstVariable
*/
var name = "Mike";                 // String w/ double quotes
var occupation = 'programmer';     // String w/ single quotes

var age = 20;                      // Integer
var gpa = 2.5;                     // Floating point number

var isTall;                        // boolean true/false
isTall = true;

name = "John";

document.write("Your name is " + name);

Casting and Converting

Copydocument.write( 100 + Number("25") + "<br>");
document.write( 100 + parseInt("50") + "<br>");
document.write( 100 + parseFloat("50.99") + "<br>");

Strings

Copyvar greeting = "Hello";
//   indexes:   01234

document.write( greeting.length + "<br>" );
document.write( greeting.charAt(0) + "<br>"  );
document.write( greeting.indexOf("llo") + "<br>"  );
document.write( greeting.indexOf("z") + "<br>"  );
document.write( greeting.substring(2) + "<br>"  );
document.write( greeting.substring(1, 3) + "<br>"  );

Numbers

Copydocument.write( 2 * 3 + "<br>" );       // Basic Arithmetic: +, -, /, *
document.write( 2**3 + "<br>" );        // Exponents
document.write( 10 % 3 + "<br>" );      // Modulus Op. : returns remainder of 10/3
document.write( 1 + 2 * 3 + "<br>" );   // order of operations
document.write(10 / 3.0 + "<br><br>");      // int's and doubles


var num = 10;
num += 100;                              // +=, -=, /=, *=
document.write(num + "<br>");

num++;
document.write(num + "<br><br>");

// Math class has useful math methods
document.write( Math.pow(2, 3) + "<br>" );
document.write( Math.sqrt(144) + "<br>" );
document.write( Math.round(2.7) + "<br>" );

User Input

Copyvar name = window.prompt("Enter your name: ");
alert("Your name is " + name);

Accessing HTML

index.htmlCopy
<h1 id="myHeader" giraffe="Giraffe Attr">GOUP</h1>
<script src="script.js"></script>

script.jsCopy
var header = document.getElementById("myHeader");
header.style="color:blue; background-color:red;"
document.write( header.getAttribute("giraffe") );
header.innerHTML = "Elephant Academy";

Arrays

Copy// luckyNumbers = [];
luckyNumbers = [4, 8, 15, 16, "twenty", false];
//  indexes:    0  1  2   3      4        5

luckyNumbers[0] = 90;
document.write(luckyNumbers[0] + "<br>");
document.write(luckyNumbers[1] + "<br>");
document.write(luckyNumbers.length);

2 Dimensional Arrays

CopynumberGrid = [ [1, 2], [3, 4] ];
numberGrid[0][1] = 99;

document.write(numberGrid[0][0] + "<br>");
document.write(numberGrid[0][1] + "<br>");

Array Functions

Copyfriends = new Array();
friends.push("Oscar");
friends.push("Angela");
friends.push("Kevin");

// friends.pop();
document.write( friends + "<br>" );
document.write( friends.indexOf("Angela") + "<br>" );
document.write( friends.indexOf("Z") + "<br>" );
document.write( friends.reverse() + "<br>" );
document.write( friends.sort() + "<br>" );

Objects

Copyvar student = {
     name: "Jim",
     major: "Business",
     age: 19,
     gpa: 2.5
};

student.name = "Andy"
document.write( student.name + "<br>" );
document.write( student.major + "<br>" );
document.write( student.gpa + "<br>" );

Functions

Copyvar sum = addNumbers(4, 60);
document.write(sum);

function addNumbers(num1, num2){
     return num1 + num2;
}

Inline Event Listeners

https://www.w3schools.com/jsref/dom_obj_event.asp

index.htmlCopy
<h1 id="myHeader" onclick="handleClick(this)">GOUP</h1>
<script src="script.js"></script>

script.jsCopy
function handleClick(element){
     alert("Clicked " + element.id);
}

Programatic Event Listeners

https://www.w3schools.com/jsref/dom_obj_event.asp

index.htmlCopy
<h1 id="myHeader">GOUP</h1>
<script src="script.js"></script>

script.jsCopy
var header = document.getElementById("myHeader");

header.addEventListener("click", function(){
     alert("You clicked " + header.id);
});

If Statements

Copyvar isStudent = false;
var isSmart = false;

if(isStudent && isSmart){
     document.write("You are a student");
} else if(isStudent && !isSmart){
     document.write("You are not a smart student");
} else {
     document.write("You are not a student and not smart");
}
document.write("<br>");

// >, <, >=, <=, !=, ==
if(1 > 3){
     document.write("number comparison was true");
}
document.write("<br>");

if("dog" != "dog"){
     document.write("string comparison was true");
}

Switch Statements

Copyvar myGrade = "A";
switch(myGrade){
     case "A":
          document.write("You Pass");
          break;
     case "F":
          document.write("You fail");
          break;
     default:
          document.write("Invalid grade");
}

While Loops

Copyvar index = 1;
while(index <= 5){
     document.write(index);
     index++;
}

index = 1;
do{
	document.write(index);
	index++;
}while(index <= 5);

For Loops

Copyfor(var i = 0; i < 5; i++){
     document.write(i);
}

var luckyNums = [4, 8, 15, 16, 23, 42];
luckyNums.forEach(function(luckyNum){
     document.write(luckyNum + "<br>");
});

Exception Catching

Copytry{
     // throw "Something went wrong"
     var x = y + 9;
}catch(err){
     document.write(err)
}finally{
     // this code always gets executed
}

Classes and Objects

Copyclass Book{
     constructor(title, author){
          this.title = title;
          this.author = author;
     }

     readBook(){
          document.write("Reading " + this.title + " by " + this.author);
     }
}

var book1 = new Book("Harry Potter", "JK Rowling");

document.write(book1.title + "<br>");
book1.readBook();

Getters and Setters

Copyclass Book{
     constructor(title, author){
          this.title = title;
          this.author = author;
     }

     get title(){
          document.write("<p>getting</p>");
          return this._title;
     }

     set title(title){
          document.write("<p>setting </p>");
          this._title = title;
     }

     readBook(){
          document.write("Reading " + this.title + " by " + this.author);
     }
}

var book1 = new Book("Harry Potter", "JK Rowling");

document.write(book1.title + "<br>");
book1.readBook();

Inheritance

Copyclass Chef{

     constructor(name, age){
          this.name = name;
          this.age = age;
     }

     makeChicken(){
          document.write("The chef makes chicken <br>");
     }

     makeSalad(){
          document.write("The chef makes salad <br>");
     }

     makeSpecialDish(){
          document.write("The chef makes a special dish <br>");
     }
}

class ItalianChef extends Chef{

     constructor(name, age, countryOfOrigin){
          super(name, age);
          this.countryOfOrigin = countryOfOrigin;
     }

     makePasta(){
          document.write("The chef makes pasta <br>");
     }

     // overridden
     makeSpecialDish(){
          document.write("The chef makes chicken parm <br>");
     }
}

var myChef = new Chef("Gordon Ramsay", 50);
myChef.makeChicken();

var myItalianChef = new ItalianChef("Massimo Bottura", 55, "Italy");
myItalianChef.makeChicken();
document.write(myItalianChef.age);