JavaScript Events and Methods Quiz
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Questions and Answers

What does the preventDefault() method do?

  • It refreshes the page.
  • It stops the default behavior of the element on which the event was triggered. (correct)
  • It initiates the default behavior of the event.
  • It adds a new event listener.

    • The preventDefault() method can be invoked on any JavaScript object.

    False (B)

    Why is it important to include a page in the href attribute even when using JavaScript?

    For accessibility reasons.

    The method _____ can be used to prevent the default action of a click event.

    <p>preventDefault</p> Signup and view all the answers

    Match the following events with their default behaviors:

    <p>Click on a link = Navigates to a new page Form submission = Sends data to a server Refresh button = Reloads the current page Checkbox toggle = Changes the checkbox state</p> Signup and view all the answers

    What does e.target represent in an event?

    <p>The element that originated the event (A)</p> Signup and view all the answers

    E.currentTarget refers to the element that originated the event.

    <p>False (B)</p> Signup and view all the answers

    What function is called when the anchor element is clicked in the provided code?

    <p>doSomething</p> Signup and view all the answers

    In the event handler, e.preventDefault() is used to prevent the ______ action.

    <p>default</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>e.target = Element that originated the event e.currentTarget = Element with the event handler bound init = Function called once DOM is fully loaded doSomething = Function executed on event trigger</p> Signup and view all the answers

    What is the recommended method to bind events to an element?

    <p>.addEventListener() (A)</p> Signup and view all the answers

    It is acceptable to hard-code all lost events in a project.

    <p>False (B)</p> Signup and view all the answers

    What should you do to initiate event binding after the DOM has loaded?

    <p>Use document.addEventListener('DOMContentLoaded', init);</p> Signup and view all the answers

    When binding an event, it is essential to know what type of event is being __________.

    <p>triggered</p> Signup and view all the answers

    Match the following event questions to their purpose:

    <p>Which element triggers the event? = Identifies the source of the event What type of event is it? = Specifies the event action What needs to happen when the event occurs? = Defines the event handler function</p> Signup and view all the answers

    Which element is used to trigger an event in the example?

    <p>#shoppingcart (B)</p> Signup and view all the answers

    Event delegation is a good practice when handling events in JavaScript.

    <p>True (A)</p> Signup and view all the answers

    What is the first step in the two-step process after the DOM has loaded?

    <p>Wait until the DOM tree has loaded in-memory.</p> Signup and view all the answers

    Which of the following methods can be used to access data attributes in JavaScript?

    <p>getAttribute() (A), querySelector() (B)</p> Signup and view all the answers

    An arrow function can only be used when a function does not require any parameters.

    <p>False (B)</p> Signup and view all the answers

    What is the purpose of the 'dataset' property in JavaScript?

    <p>To access data attributes directly using the dataset collection.</p> Signup and view all the answers

    In JavaScript, an anonymous function can be written as _____(a) => a + 100;

    <p>arrow</p> Signup and view all the answers

    Match the following JavaScript function types with their descriptions:

    <p>Anonymous function = Does not have a name and can be defined on the fly Named function = Regular function declaration with a name Arrow function = Shorter syntax for writing functions, defined with =&gt; Function expression = A function defined within an expression context</p> Signup and view all the answers

    When should you preferably use a named function?

    <p>When the function is complex and needs to be reused (C)</p> Signup and view all the answers

    The following is an example of a valid anonymous function: function showMessage(e) {}

    <p>False (B)</p> Signup and view all the answers

    How do you add a click event listener to a button element in JavaScript?

    <p>Use document.querySelector('button').addEventListener('click', function() {});</p> Signup and view all the answers

    What happens when stopImmediatePropagation() is called during an event?

    <p>No remaining listeners will be called. (A)</p> Signup and view all the answers

    Event capturing fires on the innermost element first.

    <p>False (B)</p> Signup and view all the answers

    What parameter must be added to the addEventListener() method to enable event capturing?

    <p>true</p> Signup and view all the answers

    In event capturing, the event propagates from the ______ to the child.

    <p>parent</p> Signup and view all the answers

    Match the method with its function:

    <p>stopPropagation() = Prevents further propagation of the current event stopImmediatePropagation() = Halts all remaining listeners for the current event addEventListener() = Attaches an event handler to an element preventDefault() = Prevents the default action of an event</p> Signup and view all the answers

    What is a key consideration when implementing event capturing?

    <p>Clearly state why capturing is used instead of bubbling. (B)</p> Signup and view all the answers

    Listeners of the same type can fire on parent elements when stopPropagation() is called.

    <p>False (B)</p> Signup and view all the answers

    Describe a potential downside of using event capturing indiscriminately.

    <p>It can confuse developers due to reversed event flow.</p> Signup and view all the answers

    Which type of function is recommended for reuse and legibility in most cases?

    <p>Named function (B)</p> Signup and view all the answers

    Arrow functions can be used when the name of the function is deemed unnecessary.

    <p>True (A)</p> Signup and view all the answers

    When would you prefer using the close method in DOM manipulation?

    <p>When you need to traverse the DOM tree upwards to find the nearest matching parent.</p> Signup and view all the answers

    You can dynamically add items to a list using the event object property, ___ .

    <p>e.target</p> Signup and view all the answers

    What is the key takeaway for deciding when to use a named versus an anonymous function?

    <p>Use named functions for reuse and clarity, and anonymous for one-off functions. (A)</p> Signup and view all the answers

    Using the parentNode property is favored over the closest function for DOM traversal.

    <p>False (B)</p> Signup and view all the answers

    What does the closest function do?

    <p>Travels up the DOM tree to find the nearest parent matching a specified selector.</p> Signup and view all the answers

    Flashcards

    preventDefault()

    The preventDefault() method stops the default behavior of an event. For example, clicking a link will not navigate to the specified URL.

    Event Object

    The event object is a special object that contains information about the event that triggered a function. It's often passed as an argument to event handler functions.

    Event Listeners

    Event listeners are functions that are executed when a specific event occurs on an HTML element. They allow JavaScript to react to user interactions or changes within the web page.

    addEventListener()

    The addEventListener() method adds an event listener to an HTML element. It takes two arguments: the event type and the function to be executed when the event occurs.

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    JavaScript Accessibility

    For accessibility reasons, it's crucial to ensure web applications function without JavaScript. Though the experience might be simplified, essential features should still be accessible.

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    e.target

    The HTML element where an event was triggered (e.g., the clicked button).

    Think of the clicked button or input field.

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    e.currentTarget

    The HTML element where the event listener is attached (e.g., the div containing the button).

    It's the element where you added the 'click' event listener.

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    Event Bubbling

    Events like clicks can bubble up through the DOM tree.

    Think of an event like a ripple in a pond, spreading outwards.

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    e.target vs e.currentTarget

    e.target is the innermost element triggered by the event, while e.currentTarget is the element where the event listener is attached.

    Think of the element you directly interacted with vs. the element with the "ears" listening for the event.

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    Dynamic Data

    Dynamic data means information changes in real-time. Think of a website showing live stock prices or scores.

    Web applications are usually dynamic, loading and updating content from web servers without needing to reload the entire page.

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    Event Capturing

    A mechanism for event propagation where the event fires on the outermost element first, then on progressively more nested elements until the target is reached.

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    stopImmediatePropagation()

    A method that prevents any more listeners from being called during event propagation, regardless of whether they are on the same element, parent elements, or child elements.

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    stopPropagation()

    A method that prevents any more listeners from being called during event propagation, on the same element, or parent elements.

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    Event Propagation

    When an event occurs on an element, listeners of the same type might be attached to both the element itself (target) and possibly its ancestor elements.

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    Data Attributes

    Attribute that stores information about an HTML element, prefixed with 'data-' and a custom name, e.g., data-semester.

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    Anonymous Function

    A JavaScript function that is not assigned to a specific variable. It's often used as a callback function when the name isn't important.

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    Arrow Function

    A compact function notation in JavaScript using the => (arrow) symbol. It's a shorter alternative to traditional function syntax.

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    getAttribute()

    A method in JavaScript used to retrieve the value of a data attribute from an HTML element.

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    dataset

    A special collection of data attributes available on HTML elements in JavaScript. Access data attribute values using a dot notation.

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    Function Declaration

    The process of defining a function in JavaScript. It's how you create reusable blocks of code.

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    Named Function

    A function in JavaScript that is assigned to a variable, giving it a name that can be used throughout the code.

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    Object Oriented Programming (OOP)

    An approach to programming where code is organized into objects containing data and functions, enhancing code reusability and structure.

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    Event Binding

    The process of attaching an event listener to a specific element in the Document Object Model (DOM). It allows you to execute a predefined function when a particular event occurs, such as a click or a mouseover.

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    Event Delegation

    A recommended practice to attach event listeners to a parent element instead of individual elements. It enhances efficiency and maintainability by handling events for multiple child elements using a single event listener.

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    addEventListener Method

    A method used to attach an event listener to an element in the DOM. You specify the type of event (click, mouseover, etc.) and the function to execute when the event occurs.

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    closest()

    A method that searches the DOM tree upwards until it encounters the nearest ancestor element matching the given selector.

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    Event Handler Function

    The function to be executed when an event occurs on an element. The function usually contains the logic to perform the desired action.

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    parentNode

    A function that returns the parent node of a given HTML element.

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    DOMContentLoaded Event

    The stage at which the DOM tree has been fully loaded into memory, allowing you to manipulate elements and interact with them. The DOMContentLoaded event signals the readiness of the DOM.

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    Two-Step Process for Event Binding

    A sequence of steps to ensure that event listeners are attached to elements after the DOM tree has been fully loaded. This ensures the listeners can be attached to the correct elements.

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    Rebinding Elements

    A common mistake in event binding where event listeners are hardcoded to specific elements. This approach can lead to code complexity and maintenance issues, especially when dealing with dynamic content.

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    Study Notes

    Event Bubbling

    • Event bubbling is a propagation method where an event, triggered on an inner element, successively moves up the DOM tree to its parent elements.
    • This propagates to all ancestors until the root element.

    Event Capturing

    • Event capturing is the opposite of bubbling.
    • Events start at the parent and move down successively through the child elements until the innermost element.
    • It's useful when needing to handle events on multiple nested elements in a specific order.

    Stop Propagation

    • Prevents further propagation of the current event throughout the DOM tree.
    • It doesn't prevent default behaviors from occuring.

    Stop Immediate Propagation

    • Prevents further propagation of the event to other listeners on the same element, even along any ancestral line.

    Event Object

    • Every event handler automatically receives an event object.
    • This object holds relevant information such as the event's origin, its parent, and coordinates.

    PreventDefault()

    • This method helps stop the default behavior of an HTML element.
    • It's crucial for handling events that would otherwise cause unwanted defaults, like page reloads or form submissions.

    DOM Element Selection

    • document.querySelector() selects only the first matching element.
    • document.querySelectorAll() returns all elements matching a given selector.

    Dynamic Data and Event Handlers

    • Dynamically added elements will not have associated event handlers anymore.
    • Event delegation is the solution to this problem.

    Event Delegation

    • Event delegation is a technique where event handlers are attached to a parent element rather than to individual child elements, so it can handle events that are triggered on new elements, ensuring they continue to be handled correctly.

    Static vs Dynamic Data

    • Static data is predefined HTML content.
    • Dynamic data is updated or inserted based on external information, for example through an API.

    Iterations with JavaScript

    • JavaScript offers several built-in functions that iterate over arrays. Using a forEach() , or for...of loop is preferred over a simple for loop.

    Function Reusability

    • Functions improve code reusability by enabling the same block of code to be executed at various points.

    Function Call

    • Calling a function starts its execution.
    • The values written within the function body modify the arguments to the function.

    Function Parameters

    • Values passed to functions are called parameters or arguments.
    • Modifying variable values within a function won't modify the original variables outside the function.

    Event Handling

    • e.preventDefault() method stops the default behavior of an event.
    • This is ideal when you want to prevent a default action—such as a page reload—associated with a specific event, like a form submission or a link click, without interfering with other handlers.

    Event Properties

    • e.target retrieves the exact element that triggered the event and the e.currentTarget is the element the event listener is tied to.

    DOM Scripting

    • DOM scripting is the use of JavaScript to modify or access HTML elements.

    HTML Data Attributes

    • HTML data attributes are used to store custom data linked to HTML elements.

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    Description

    Test your knowledge on JavaScript event handling and methods like preventDefault(). This quiz covers essential concepts such as event binding, default behaviors, and key event properties. Perfect for those looking to deepen their understanding of JavaScript interactions.

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