JavaScript I

INFO 253A: Front End Web Architecture

Kay Ashaolu


  • A fully featured programming language
  • Used to be only for the browser, used along with HTML and CSS
  • Now used on web servers and for Application Program Interfaces (APIs)
  • Great example of composability!

Why learn JavaScript first?

  • Truthfully, front end development is heavily dependent on JavaScript
  • If a site doesn't need JavaScript, chances are that there's some low code tool that can produce the site without needing to know code
  • Demonstrates the software engineering skills needed now to become a frontend engineer

JavaScript: Powering your pages

  • JavaScript brings a website to life
  • No need for a server to execute by the browser
  • Pop-ups, drop down navigation
  • Form validation, animation
  • Application development

JavaScript: Powering your Servers

  • JavaScript is used to power the servers that launch websites! (NodeJS)
  • No longer considered a "play" language

JavaScript: Powering your APIs

  • API: Application Program Interface
    • We will not cover this in this class
  • JavaScript is not just reserved for building web pages
  • JavaScript can power pure back end functionality

We will be using JavaScript

  • To build our website
  • To power interactivity between the user and the website
  • To communicate to external servers using APIs

So let's learn some JavaScript

  • We are going to use our browsers to run our JavaScript
  • This will be a little weird at first, but remember that the browser is the "executor" of the code that you write on the frontend
  • Once we learn HTML/CSS, it will be more apparent how all of these technologies work together

What this is not

  • This is not an exhaustive review of the JavaScript programming language
  • One goal is to get you familiar with the features of the language
  • Another goal is to give you the opportunity to ask questions
  • The better you know pure JavaScript, the more you'll be able to build rich web applications
  • Again, even though we are learning React in this course, the better you know the JavaScript language, the better you will understand React

Before we start: code editor

  • You will need an editor that can save files in plain text
  • Better if you find something that can highlight code to make it much more readable
  • My tool of choice (currently): Visual Studio Code

How to run JavaScript

  • Create an HTML file called "index.html"
  • Add the following text in the file:
		<title>Learning JavaScript</title>
		<script src="script.js"></script>

What did we just do?

  • You just created an HTML file that is blank, but tells the browser to execute "script.js", located in the same location as this html file
  • Remember the HTML file is the first content to get to the browser to be parsed to build the DOM. 
  • Next, because the "script" tag is present, it signals to the browser to retrieve "script.js", so another request is made to retrieve that
  • Once it is received, "script.js" is executed line by line

Variables? Data Types?

  • A variable is an empty space holder for a future value
  • There are a few types of values that JavaScript uses
    • Numbers and Booleans (true or false)
    • Strings or a sequence of characters
    • Functions
    • Arrays (lists of variables) and Objects


  • Declare with let to scope correctly
  • Weak, dynamic typing


let a = 3;
let b = 5;
let c = a + b;


let a = "hello";
let b = "world!";
let c = a + b;

Arrays (Lists)

let list = [2,3, "KAY"];


let titles = {
    info253: 'Web Arch',
    info256: 'Applied NLP'

let schools = {
    berkeley: {info253: 'Web Arch'},
    stanford: {cs101: 'Intro CS'}

But Note

  • We will go over all of these types through writing functions
  • You don't have to do this, but you should do this
  • It is extremely important to be comfortable with writing and using functions


So what is a funciton

  • Think of a function as a black box, where you put things in (inputs) and out comes a result (output)
  • It's a black box because you don't necessarily need to know how it's converting the inputs
  • The parameters are the inputs, the return statement defines the output

Function Syntax

let add = function(a, b) {return a + b;}
let c = add(2, 7)
/* c is now 9 */

let arithmetic = {add: add, subtract: function(a, b) {return a - b;}};
let d = arithmetic.subtract(11, 4);
let e = arithmetic.add(0, 3);
/* d is now 7; e is now 3; */

Our First Function

function helloWorld(first_name, last_name) {
	let message = "Hello World " + first_name + " " + last_name;
	return message;

let first = prompt("Enter your first name");
let last = prompt("Enter your last name");
let output = helloWorld(first, last);

Our First Function

Our First Function

What does this function do?

What did that function do?

  • Declared a function that we put in two values or inputs: (first name and last name)
  • The function declared a variable (message) that contains the string "Hello World [your first name] [your last name]"
  • After it's done, it will produce one value or output: (the message) and return it
  • We ask the user for their first and last name, and print out the result from the function

More to come​

  • Conditionals
  • For and While loops
  • Arrays
  • Objects 

For the non programmers here stay with me, learn this and it will empower you throughout this course and beyond