JavaScript Chapter 1 - Introduction to JavaScript

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Questions and Answers

What is the correct syntax to register an event handler for an element in the bubbling phase using addEventListener?

element.addEventListener(‘eventname’,eventhandler,false); (correct)

element.addEventListener(‘eventname’,eventhandler);

element.addEventListener(‘eventname’,eventhandler,true);

element.addEventListener(‘eventname’,eventhandler,1);

Which of the following properties of an event object allows access to the X coordinate of the mouse relative to the client area?

clientX (correct)

keycode

altLeft

clientY

What is event handling in JavaScript?

Stopping any ongoing actions on a page.

Executing code based on user-triggered events. (correct)

Running code when the page is loaded.

Performing background tasks without user interaction.

What are the two phases of event handling in the W3C Event Propagation Model?

Event Capturing and Event Bubbling Signup and view all the answers

Which of the following elements can trigger the 'click' event?

Button Signup and view all the answers

Which method can be used to cancel the bubbling phase of an event?

event.cancelBubble = true; Signup and view all the answers

In the context of the Document Object Model (DOM), what does DOM primarily represent?

The structure and properties of HTML documents Signup and view all the answers

Which event is associated with the 'focus' event handler?

Input being selected or activated. Signup and view all the answers

Which of the following statements about JavaScript and the HTML DOM is NOT correct?

JavaScript can directly influence server-side variables. Signup and view all the answers

What is the purpose of the event object in JavaScript?

To represent a user-triggered event and provide details about it. Signup and view all the answers

How do you create an empty array in JavaScript?

let colors = []; Signup and view all the answers

What will the expression colors.length return if colors is defined as let colors = new Array('red', 'blue', 'green');?

3 Signup and view all the answers

What property is used to attach an event handler in JavaScript?

onclick Signup and view all the answers

What does the keycode property of an event object represent?

The code of the key that was pressed during a keyboard event Signup and view all the answers

Which of these events is not interactive?

load Signup and view all the answers

Which method would you use to remove the last element from an array?

pop() Signup and view all the answers

What is the primary purpose of the HTML DOM?

To structure the web pages and allow interaction with JavaScript Signup and view all the answers

What is the result of the following invocation: let colors = ['red', 'blue', 'green']; colors[3];?

undefined Signup and view all the answers

Which element would produce a 'change' event?

Checkbox Signup and view all the answers

How is the event handler typically defined in JavaScript?

It is provided as a function assigned to the element's property. Signup and view all the answers

Which syntax correctly defines a function in JavaScript?

function name(arg1,arg2) { //code } Signup and view all the answers

What is a key characteristic of JavaScript objects?

They are a collection of related properties and methods. Signup and view all the answers

What will happen when the shift() method is called on an array?

It removes the first element and shifts all elements. Signup and view all the answers

Which of the following statements is true about invoking a JavaScript function?

A function can be invoked in multiple ways. Signup and view all the answers

Why does JavaScript need to interact with the DOM instead of directly understanding HTML tags?

JavaScript is designed to work with object representations, not markup. Signup and view all the answers

What does the method hasChildNodes() return when called on a node without children?

false Signup and view all the answers

Which method is NOT used to access elements in the DOM?

querySelector() Signup and view all the answers

How can you change the inner HTML of an element using JavaScript?

element.innerHTML = newHtmlContent Signup and view all the answers

Which method allows you to create a new HTML element in the DOM?

document.createElement(element) Signup and view all the answers

What is the purpose of the appendChild() method in the DOM?

To add a new child element to a parent node. Signup and view all the answers

What would document.body.firstChild.hasChildNodes() return if firstChild is a text node?

false Signup and view all the answers

How do you assign a function to an element's onclick event in JavaScript?

element.onclick = function(){ // code } Signup and view all the answers

What is a key functionality of JavaScript in web pages?

Validating forms and creating interactive elements Signup and view all the answers

Which of the following best describes a JavaScript engine?

A component of browsers that executes JavaScript code Signup and view all the answers

What is one advantage of using external JavaScript files?

They can increase the overall page loading speed due to caching. Signup and view all the answers

How should JavaScript be included in an HTML document?

Use the <script> tag with the src attribute for external files. Signup and view all the answers

What happens to the JavaScript code when a web page is loaded?

The JavaScript engine executes the code after HTML and CSS are loaded. Signup and view all the answers

Which part of a web browser is responsible for interpreting JavaScript code?

The JavaScript engine Signup and view all the answers

What file extension is commonly used for JavaScript files?

.js Signup and view all the answers

Why might embedded JavaScript be displayed as normal text in a browser?

If the JavaScript code is incompatible with the browser. Signup and view all the answers

Study Notes

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.

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Description

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.