JavaScript Introduction Notes

Frequently Asked Questions

1. What is JavaScript?

   • One of the most popular programming languages.
   • Used by companies like Netflix, Walmart, and PayPal.
   • Average salary in the U.S.: $72,000/year.
   • Roles: Front-end, Back-end, Full Stack Developer.

2. What can you do with JavaScript?

   • Initially used for interactive web pages.
   • Can build web/mobile apps, real-time networking apps (chats, video streaming), command-line tools, and games.

3. Where does JavaScript code run?

   • Originally in browsers (JavaScript engines like SpiderMonkey in Firefox and V8 in Chrome).
   • Node.js allows execution outside of browsers, enabling backend development.

4. What is the difference between JavaScript and ECMAScript?

   • ECMAScript is a specification; JavaScript is a programming language based on this specification.
   • ECMAScript versions have been updated annually, with ES6 (2015) introducing many new features.

Writing JavaScript Code

• JavaScript can be written in the console of any browser (e.g., Chrome).
• Basic syntax example:

  console.log('Hello World');  
  

• Use semicolons to terminate statements.

Setting Up Development Environment

1. Code Editor:
   • Recommended: Visual Studio Code (download from code.visualstudio.com).
   • Alternatives: Sublime Text, Atom.
2. Node.js:
   • Download from nodejs.org.
   • Use Node.js for installing third-party libraries.

Creating a Project

1. Create a folder named js-basics.
2. Drag and drop it into Visual Studio Code.
3. Create a new file index.html and add basic HTML boilerplate.
4. Install Live Server extension in VS Code for serving applications.
5. Create a new file index.js for JavaScript code.
6. Reference index.js in index.html:

   <script src="index.js"></script>  
   

JavaScript Basics

Variables

• Used to store data temporarily.
• Declaration: let name; (modern best practice)
  • Use const for constants (values that don't change).
• Variable Naming Rules:
  1. Cannot use reserved keywords.
  2. Must be meaningful.
  3. Cannot start with a number.
  4. Cannot contain spaces or hyphens (use camelCase).

Primitive Types

1. String:
   • Example: let name = 'Mosh';
2. Number:
   • Example: let age = 30;
3. Boolean:
   • Example: let isApproved = true;
4. Undefined:
   • Default value of uninitialized variables.
5. Null:
   • Explicitly empty value.
6. Symbol:
   • New in ES6 (not covered in detail).

Dynamic Typing

• JavaScript is a dynamic language; variable types can change at runtime.

Objects

• Used to group related data:

  let person = {  
      name: 'Mosh',  
      age: 30  
  };  
  

• Accessing properties:
  • Dot notation: person.name
  • Bracket notation: person['name']

Arrays

• Used to store lists of items:

  let colors = ['red', 'blue'];  
  

• Accessing elements using indices: colors[0].
• Arrays can hold different types of data.

Functions

• A block of code that performs a task:

  function greet(name) {  
      console.log('Hello ' + name);  
  }  
  greet('Mosh');  
  

• Can take parameters and return values.

Conclusion

• This introduction covers the basics and prepares for more advanced topics in JavaScript.
• Encouragement to enroll in the complete JavaScript course for deeper learning.