Week 3

Scripting For The Web
Sep 16, 2020


Today’s questions

Warmup: CSS animation

CSS animation resources


HTML is for content. CSS is for style. JavaScript is for interaction.

HTML + CSS + Javascript cake

Javascript as a name was selected because the Java language was popular at the time. They are not otherwise related. Over time Javascript was adopted by all browsers though each browser/engine may have its own implementation. Standards for JavaScript are maintained by an international committee and the standard is known as EcmaScript.

Javascript is a multiparadigm language, meaning there are many approaches to coding with it.

Javascript is weakly typed, meaning that the language does not have built in safety checks for memory and variable types. It is evaluated just in time. In contrast to Processing, for example, which is compiled (and checked for errors) before running.

Javascript as a language has evolved significantly over time. New language features have been implemented and adopted at varying times by different browsers. Ecmascript2015 aka ES6 brought significant changes to syntax for classes, types, functions and loops, among other changes.

Javascript includes support for working with text, arrays, dates, regular expressions, and basic manipulation of the DOM.

What makes Javascript special?

Technically, Javascript is a scripting language in a host environment, which means that many applications or host environments can provide their own systems for accessing and executing it. Javascript can be used in web browsers but also in Adobe products, system software, embedded computers, databases, and other environments. It is increasingly used as the language that underlies the internet of things, so that tens of millions of devices can be accessed and controlled via Javascript.

Where to use Javascript

Advantages of External scripts

<script src="myScript1.js"></script>
<script src="myScript2.js"></script>

Accessing the browser console

Chrome console

accessing the browser console - Chrome
Accessing the console in Chrome

Firefox console

accessing the browser console - Firefox

Safari console (2 parts!)

In Safari, you must first go to File > Preferences and choose the Advanced tab and turn on the Developer tools. This will add a Developer Menu.

accessing Developer Tools in Safari

Now you can access the console.

accessing the console in Safari

Hello World in Javascript

Normally, you’ll have your Javascript code acting on your website, handling events (the mouse, page load, etc) or responding to input for example.

This isn’t the normal use of JavaScript, but as a beginner it’s helpful to know that JavaScript can produce some output very simply, in a few different ways:

Hello World is typically the first program you write in a programming language when you are testing it out. It tells you whether you can get a basic program to run. A typical Hello World program in Javascript could use any of the 4 above methods.

Entering Javascript directly in the console

Open the Javascript web console. Here you see error messages and warnings from the site you are viewing. You can also enter code directly and press enter and it will execute.

console.log('Hello World');

This will print Hello World as output.

console.log looks really ugly. If it helps, think of it as saying print out.

Placing Javascript within script tags

Leave your console open.

Go back to your index.html file or make a new one.

In your page somewhere add the opening and closing script tags, and put some basic Javascript code in there to print text on the console.

  console.log('This will print out in the console');

Now reload the page in the browser and look at the console. The statement should be printed there.

Using an external Javascript file

Just like we do with an external css stylesheet it’s best practice to use an external Javascript file that you call in your html file. Most of the time you will want to put this script near the end of your page right before the closing </body> tag. We do this so our page content loads (text, images…) before our script runs so there is something to see if our site loads slowly.



<!DOCTYPE html>
    <title>Testing the console</title>
    <h1>Hello World</h1>
    <script src="main.js"></script>


console.log('Hi. From an external script');

Check the web console to confirm the text from main.js printed in the console.

Javascript Syntax

Javascript code starts executing instructions in order.


Comments are notes to yourself or other programmers. The browser skips it. In addition to writing helpful notes for when you reopen your software after a break, it can be helpful to use commenting to turn on and off different lines of code.

//this is a comment
this is
a multi line
comment. I don't use them very much


Semicolons ; are generally used to end executable statements. You can even use them to have multiple statements on a single line of code. The semicolons are optional when each line has a single statement, but it’s good practice to use them anyway.

var message = "some text";

Data Types

Variables are used to store data for later. Javascript is a weakly typed language. You don’t need to declare a variable’s type and there is no error checking.

JavaScript variables can hold many data types: numbers, strings, objects and more (including functions, which we’ll get to later). Unlike other languages, you can use var to declare all variable types. Note that you don’t specify an integer nor float.


var age = 21;   // Number
var weight = 145.3; // Number
var name = "Cardi B";  // String
var person  = {firstName:"Dwayne",
 middleName:"The Rock",
 lastName:"Johnson"};    // Object

Now that those variables are set, we can use them.

console.log("Quiet, I'm listening to "+name);

Notice how I broke up The Rock’s name above to make it easier for me to read. Javascript collapses all spaces, lines, tabs that are bigger than a space into a single space.

Some other values


More about Variables


Functions are code blocks

function myFunction() {
    var contents = $('#contents');

    $('#demo1').html("Hello World");

Control Structures

Basic if statement

if (name === 'Belcalis Marlenis Almanzar'){
    console.log(name+", also known as Cardi B.");

More complex if statements

if (name === 'Quavo'){
  console.log('Right on');
} else if (name === 'Offset'){
} else if (name === 'Takeoff'){
} else {
  console.log('Hold on, who are you?');



More JavaScript


students = [

You can access an array by specifying the index.

  console.log(students[0]); //prints out 'Jonathan'

Arrays have length


The length is the total number of entries. It’s common to access or do something with the contents using a loop.

console.log('The Students are: ');

for (let i=0; i < students.length; i++){

Note: The last entry to an array is not arrayName[arrayName.length]; Remember that if we have an array with 5 entries, we will have an index 0, 1, 2, 3, 4. The last entry is therefore arrayName[arrayName.length-1];

For loops

var genres = ['Bebop', 'Rocksteady', 'Dub', 'Ska'];

//looping through an array
for (let i = 0; i < genres.length; i++) {


Now that we understand the basics of Javascript, let’s consider what it can do:

The HTML DOM is a standard for how to get, change, add, or delete HTML elements.

DOM stands for Document Object Model.

HTML elements are objects.
Their properties can be changed.
We have different methods for accessing these.
We can have our HTML change based off specific events (a page opening, resizing, mouse pressed, etc.)


The DOM works like a tree, with nodes branching off that below. We can work on these nodes, remove them, add to them, change their properties, etc.