JavaScript Chapter 1 - Introduction to JavaScript

Introduction to JavaScript

• JavaScript enhances web functionality, interacting with HTML and CSS.
• Dynamically updates web interface post HTML and CSS loading using the JavaScript engine, responsible for code execution.
• Major JavaScript engines include V8 (Chrome), SpiderMonkey (Firefox), and JavaScriptCore (Safari).

Including JavaScript in HTML

• Three methods to include JavaScript in an HTML page:
  • Inline using the script tag within HTML.
  • Internal within a script tag in the head or body of HTML.
  • External file with a .js extension referenced using the src attribute in the script tag.
• Benefits of external JavaScript:
  • Keeps HTML and script separate for better readability.
  • Improves maintenance and speeds up page loading via caching.
  • Hides JavaScript code from incompatible browsers.

JavaScript Arrays

• Three constructors for creating arrays:
  • Array(); creates an empty array.
  • Array(number_of_elements); initializes an array with a specified length.
  • Array(element1, element2, ...); creates an array with initial elements.
• Array properties:
  • length property determines the number of elements in an array.
• Common Array Methods:
  • toString(), at(index), join(), pop(), push(), shift(), unshift(), delete(index), concat(array2).

Functions in JavaScript

• Defined using the function keyword followed by a name and parameters.
• Syntax example:

  function name(arg1, arg2){ 
      // code to execute 
      return(result); 
  }
  

• Invocation methods include event triggers, direct calls, or self-invocation.

JavaScript Objects

• Objects consist of properties and methods, used to encapsulate related data and functionalities.
• Standard methods include stop() for halting downloads and focus() for focusing on the window.

Event Handling

• Event handling involves executing code in response to user actions (e.g., clicks, keystrokes).
• Types of events include interactive (e.g., button clicks) and non-interactive (e.g., page load).
• Event types with associated sources include:
  • click: buttons, links
  • focus: input fields, text areas
  • keypress: generally applicable across documents
• The event handler is a JavaScript function assigned to an element to respond to events.

Event Object and Propagation

• Each event creates an event object with properties such as srcElement, type, and key event handling properties like ctrlKey.
• Event propagation follows W3C specifications, segmenting into:
  • Event Capturing
  • Event Bubbling
• Use addEventListener() to register event handlers for both phases.

Document Object Model (DOM)

• DOM represents the structure and properties of an HTML document as a hierarchical tree.
• JavaScript manipulates the DOM for:
  • Dynamic updates
  • Interactivity and content changes
  • Cross-browser compatibility
• Key DOM methods for element access include:
  • getElementById(), getElementsByClassName(), getElementsByTagName().

Modifying HTML Elements

• Update HTML content via key properties and methods:
  • element.innerHTML = new_content; changes inner HTML.
  • element.setAttribute(attribute, value); updates attributes.
• Manage HTML elements with methods for creation, removal, and appending:
  • document.createElement(), document.removeChild(), document.appendChild(), document.replaceChild().

Adding Event Handlers

• Attach event handlers using document.getElementById(id).onclick = function() { /* code */ };.

These notes provide a concise overview of JavaScript's key concepts, focusing on its integration with web technologies and functionalities.

This quiz covers the basics of JavaScript, including its introduction, variables, arrays, functions, and more. It aims to enhance your understanding of how JavaScript interacts with web pages and improves functionality. Prepare to explore essential concepts and applications in web development.