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JavaScript Basics

JS Intro Introduction to JavaScript - basic output JavaScript input with prompt and confirm Variable How Computers Work - Playlist

JS Intro

JavaScript (JS) is a lightweight, interpreted, or just-in-time compiled programming language with first-class functions. While it is most well-known as the scripting language for Web pages, many non-browser environments also use it, such as Node.js, Apache CouchDB and Adobe Acrobat. JavaScript is a prototype-based, multi-paradigm, single-threaded, dynamic language, supporting object-oriented, imperative, and declarative (e.g. functional programming) styles.

Read more about JavaScript

Basic Use

• JS can be embedded or included
  • Embed = JS put directly into HTML file
    • <script> tag is used
  • Include = Line placed into HTML file that references the JS file

Basic Inputs & Outputs

Code	Does
alert()	Creates a pop-up with the alert text inside
document.write()	Changes the content on the page to what is inside the document.write() function
console.log()	Prints the contents of the console.log() call into the console for us to read
prompt()	Shows a pop-up window asking for a user’s input
confirm()	Provides a Yes or No confirmation to the user; typically paired with an IF / ELSE statement

Variables

What are Variables?

• Variables are containers for storing data values
• There are four ways to declare a variable:
  • var
  • let
  • const
  • Nothing
• Variables require an identifier
  • This is the name follow the declaration
    • Example:
      • let person = "John"
        • person is the identifier
• JS treats the following as letters, and thus as valid variable names:
  • Any letter
  • $
  • _

var x = 5;
var y = 6;
var z = x + y;
console.log(z) >> 11

When to Use const?

• As a general rule, always declare variables with const
• const cannot be accidentally modified later in the program
  • If you do try and modify a const, you will get an error message
• If a variable can change, use let

const price1 = 5;
const price2 = 6;
let total = price1 + price2;
console.log(total) >> 11