Introduction to JSON

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Questions and Answers

What is the primary purpose of JSON?

To enhance graphics in web applications

To facilitate data interchange between applications (correct)

To serve as a programming language

To store relational data in databases

Which data types are supported in JSON?

Only objects and arrays

Strings, booleans, and functions

Strings, booleans, arrays, objects, and null (correct)

Only strings and numbers

Which file extension is standard for JSON files?

.txt

.js

.xml

.json (correct)

Which is a common error when writing JSON?

Including trailing commas (B) Signup and view all the answers

What does JSON.stringify() do in JavaScript?

Converts JavaScript objects to JSON strings (C) Signup and view all the answers

What should be used to denote a JSON object?

Curly braces {} (D) Signup and view all the answers

Which statement about JSON is true?

JSON has remained stable since its creation. (C) Signup and view all the answers

When using JSON, which of the following is NOT a recommended practice?

Include comments for clarification (B) Signup and view all the answers

What is the primary purpose of the childNodes property in the DOM?

To access all child nodes, including non-element nodes (B) Signup and view all the answers

Which property would you use to access only the element children of a node, excluding text and comment nodes?

children (A) Signup and view all the answers

What does the parentNode property return for the document node?

Null (B) Signup and view all the answers

Which properties would you use to access sibling elements while skipping any text nodes?

previousElementSibling and nextElementSibling (D) Signup and view all the answers

How can you modify the content of an HTML element easily?

Using the innerHTML property (C) Signup and view all the answers

What does the textContent property provide access to?

Only the text inside the element, excluding HTML (A) Signup and view all the answers

What is the first step in adding a new HTML element using the DOM?

Creating the element (A) Signup and view all the answers

What is a common sequence of actions involved in creating and inserting an HTML element?

Creating, assigning attributes, then inserting (C) Signup and view all the answers

What is the purpose of the `setAttribute()` method in creating DOM elements?

To define attributes for an element. (D) Signup and view all the answers

How can you add a newly created link to an element with the ID 'myP'?

Use <code>appendChild()</code> method. (D) Signup and view all the answers

What is the role of the `createTextNode()` method?

To create a text node that can be added to an element. (A) Signup and view all the answers

What is one way to respond to events in the DOM?

Assigning an event handler using properties. (B) Signup and view all the answers

Which of the following is NOT true about assigning event handlers?

Function assignments require parentheses to work. (D) Signup and view all the answers

What does the `appendChild()` method do when adding an element?

Inserts the element as the last child of the parent. (B) Signup and view all the answers

In which way can you assign an event handler using DOM-0?

Assigning directly to properties like <code>element.onclick</code>. (A) Signup and view all the answers

What is a characteristic feature of a closure in JavaScript?

It is created when a function is defined within another function. (A) Signup and view all the answers

How do closures help in data encapsulation within constructor functions?

They prevent direct access to sensitive information by creating private members. (D) Signup and view all the answers

What keyword is used when creating a new object from a constructor function?

new (D) Signup and view all the answers

What is defined by lexical scope in JavaScript?

The scope of variables is determined by the order of their declaration. (C) Signup and view all the answers

What does the Document Object Model (DOM) represent?

A hierarchical representation of an HTML document. (C) Signup and view all the answers

Which of the following is a correct statement about DOM nodes?

DOM nodes can also represent text and comments in an HTML document. (D) Signup and view all the answers

What is the purpose of using closures in the uniqueId function example?

To keep track of unique identifiers across multiple calls. (D) Signup and view all the answers

What is NOT a feature of a scope created by closures?

Closure functions are always callable from anywhere. (A) Signup and view all the answers

What does the class selector in the DOM access?

The first element with a given CSS class (A) Signup and view all the answers

What will the following code return: `document.querySelector('[href]');`?

The first element that contains any href attribute (D) Signup and view all the answers

What is a significant difference between `querySelector` and `querySelectorAll`?

querySelectorAll returns all matching elements (D) Signup and view all the answers

What will `firstChild` return if there are no child elements?

A null value (B) Signup and view all the answers

Which method can be used to bypass text nodes when selecting the first child element?

firstElementChild (A) Signup and view all the answers

What does the `lastElementChild` property return when there are no element nodes?

A null value (C) Signup and view all the answers

In DOM navigation, what does `nodeName` return for a whitespace node?

#text (B) Signup and view all the answers

Which of the following is true about the attribute selector?

It can select elements with specific attributes (C) Signup and view all the answers

What happens if the same event handler is assigned multiple times to an HTML element?

Only the last assigned event handler will execute. (D) Signup and view all the answers

Which of the following parameters does the addEventListener method NOT accept?

Element ID (A) Signup and view all the answers

What is the default value of the phase parameter in the addEventListener method?

False (D) Signup and view all the answers

When detaching an event handler using removeEventListener, what must be done?

Pass the same parameters as used in addEventListener. (D) Signup and view all the answers

What is the behavior called when an event propagates from an inner element to an outer element?

Event Bubbling (D) Signup and view all the answers

If you want the parent element to handle an event before its child element, what value should be set for the phase parameter?

True (C) Signup and view all the answers

What is a significant advantage of using the addEventListener method?

It allows multiple event handlers of the same type on one element. (D) Signup and view all the answers

What type of value does the phase parameter of addEventListener expect?

Boolean (B) Signup and view all the answers

What must be done to make a newly created link visible in the document?

Insert it into the document using appendChild(). (A) Signup and view all the answers

What is the purpose of the createTextNode() method in the context of creating elements?

To create a text node that can be appended to an element. (C) Signup and view all the answers

Which method is used to insert an element as the last child of a specified parent node?

appendChild() (A) Signup and view all the answers

Which statement about event handling in the DOM is true?

DOM-0 allows event handlers to be assigned using properties of elements. (C) Signup and view all the answers

What must be ensured when assigning a function as a DOM-0 event handler?

The function should not include parentheses. (A) Signup and view all the answers

In which situations would you use the setAttribute() method?

To add or modify an attribute of an HTML element. (C) Signup and view all the answers

What happens if you call appendChild() on an existing element?

It will append the element as a new child. (D) Signup and view all the answers

Which property can be used to assign an event handler directly to a button's click event?

button.onclick (C) Signup and view all the answers

Study Notes

Closure in JavaScript

A closure in JavaScript is created when a function is defined inside another function.
It retains access to variables in its parent function's scope, even after the outer function has finished executing.
A closure allows a function to remember the environment in which it was created, including variables that were in scope at that time.
Lexical scope defines the accessibility of variables and functions based on their location within the source code. A closure maintains a reference to its lexical environment, capturing the state of the outer function at its creation time.

Example of Closure

A function createCounter is defined.
A variable count is initialized to 0 within the createCounter function.
A nested function is returned by createCounter.
The nested function increments count and returns its current value.
The nested function forms a closure because it has access to the variables in its parent function's scope.

Constructor Functions in JavaScript

In JavaScript, objects can be created using functions, often called constructor functions.
The constructor function defines the structure of the object.
The new keyword is used to create a new object from the constructor function.
The keyword this is used within the function to attach properties and methods to the new object.

Use of Closures

Closures can be used to create private members within constructor functions, ensuring data encapsulation and preventing direct access to sensitive data.

Unique Identifier Function

Using closures and immediately invoked function expressions (IIFEs), a uniqueId function can be created that returns a unique identifier each time it is called.
This function uses a counter variable that is incremented with each call and returns a string concatenating "id_" with the current counter value.

Document Object Model (DOM)

An HTML document is organized as a tree structure.
The DOM is a programming interface that allows access and manipulation of HTML code.
The document is represented as a hierarchical tree and the components are referred to as nodes.

DOM Node Types

Elements, texts, and comments are some types of DOM nodes.
Every DOM node has a nodeType property that specifies the type of the node.
- ELEMENT_NODE: Represents an HTML element.
- TEXT_NODE: Represents text within an element.
- COMMENT_NODE: Represents comments in HTML.
- DOCUMENT_NODE: The root node of the DOM tree.
- DOCUMENT_TYPE_NODE: Denotes the document type (e.g., HTML5).

Accessing the DOM in JavaScript

document.getElementById('elementId'): This retrieves a DOM element using its ID.
document.getElementsByTagName('tagName'): This retrieves all elements with a specific tag name.
document.querySelector(CSSselector): This selects the first element that matches the CSS selector in the structure of the document.
document.querySelectorAll(CSSselector): This selects all elements that match the CSS selector in the structure of the document.
DOM nodes can be manipulated using various properties and methods, enabling dynamic changes to the HTML content. For instance, the innerHTML and textContent properties can alter or retrieve the content within HTML elements.

Navigating Between DOM Nodes

Properties like parentNode, previousSibling, nextSibling, firstChild, lastChild, childNodes are used to traverse the DOM tree.
For instance, previousSibling and nextSibling allow navigation to the preceding and following sibling nodes.
childNodes returns all child nodes in the current node, whereas children returns only elements.
The firstElementChild and lastElementChild properties allow you to directly access only children nodes that are elements and not text nodes.

Changing HTML Content

The innerHTML property is used to modify the content of an HTML element.
It allows adding HTML content or getting what's already present.
The textContent property is an alternative, offering access solely to text content within elements, ignoring HTML tags.

Creating and Inserting Elements

JavaScript, using document.createElement(), creates new HTML elements in memory; these aren't appended to the page.
With attributes using setAttribute, new elements are defined.
With appendChild, these new elements are added into an HTML element.
Using createTextNode, text is added as child nodes.

Events

Events are actions conducted by users or the browser.
Event handling involves associating functions with events to respond to events.
addEventListener and removeEventListener methods are used to attach or detach event handlers, enabling dynamic responsiveness to user actions or browser events. This method has increased control over how events are handled, allowing multiple event handlers to be attached to the same event without overwriting existing functionality.
DOM-0: Older methods, where event handling properties are directly attached to elements using the on event syntax. (e.g. elem.onclick = ...).
A different method, DOM-2 allows adding several handlers for the same event in a more organized way, using addEventListener and removeEventListener. The phase parameter provides additional control, enabling events to trigger in specific order (capture or bubbling) across parent-child relationship.

JSON (JavaScript Object Notation)

A lightweight data-interchange format suitable for human and machine readability and parsing.
Widely used with web development (APIs), data storage, and various applications requiring data exchange between systems.
The structure typically uses key-value pairs; Objects are defined with curly braces {} and Arrays with square brackets []. Basic types such as strings, numbers and boolean are also supported.
JSON.stringify() converts JavaScript objects to JSON text.
JSON.parse() converts JSON text to JavaScript objects.

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Description

This quiz will test your knowledge about JSON, including its primary purpose, supported data types, and common practices. You will also explore functions like JSON.stringify() in JavaScript and learn about potential errors while writing JSON. Get ready to challenge your understanding of this data interchange format!