JavaScript Basics: Ternary, Switch, and State

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Questions and Answers

What value is returned by the ternary operator when `isAuthenticated` is false?

Please Log In

In a switch statement, what is the output for `User_Status` set to 'VERIFIED'?

Welcome User! You are Verified

What behavior does the `window.addEventListener` function implement in the provided code?

It logs the window's inner height and width on resize.

Explain what 'state' refers to in the context of a component's memory.

State is a component-specific memory that stores information and determines the component's behavior and rendering. Signup and view all the answers

What will happen if 'User_Status' does not match any defined cases in the switch statement?

It will return 'User Status Unknown'. Signup and view all the answers

What is the initial state of the `user` variable in the `App` component?

[{ id: 1, name: 'John Doe', email: '<a href="mailto:[email protected]">[email protected]</a>' }, { id: 2, name: 'Jane Smith', email: '<a href="mailto:[email protected]">[email protected]</a>' }] Signup and view all the answers

How does the `UserDetail` component determine if it is in edit mode?

It uses the <code>IsEdit</code> state variable, which toggles between true and false when the Edit button is clicked. Signup and view all the answers

What does the `useEffect` hook with the `sync` dependency do in the `App` component?

It changes the document title to 'Welcome' followed by the current value of <code>counter</code> and logs 'Rendering...' to the console. Signup and view all the answers

What is the purpose of the AbortController in the second `useEffect` of the `App` component?

It aborts the fetch request when the component unmounts to prevent memory leaks. Signup and view all the answers

How does the component update user information in the `setUser` method?

It maps through the current user state and updates the user object that matches the user's ID. Signup and view all the answers

What is the role of the `handleSubmit` function in the `BlogForm` component?

It prevents the default form submission and sends a POST request with the blog data to create a new post. Signup and view all the answers

What are the expected properties of the `user` prop in the `UserDetail` component?

The <code>user</code> prop should have <code>id</code>, <code>name</code>, and <code>email</code> properties, all of which are required. Signup and view all the answers

In the `BlogForm`, how are the title and body fields updated in state?

The title and body are updated using <code>setBlogData</code> with the previous state spread and the new values from the input fields. Signup and view all the answers

What will happen if `BlogData.title` or `BlogData.body` is empty when submitting the form?

The <code>handleSubmit</code> function will not proceed with the POST request to create a new blog post. Signup and view all the answers

What does the button that increments the `counter` variable do in the `App` component?

It increases the <code>counter</code> state by 1 each time it is clicked and updates the displayed count. Signup and view all the answers

How is the `setSync` state variable used to control the fetch operation?

Toggling the <code>setSync</code> updates the state, which triggers the <code>useEffect</code> responsible for rendering the title. Signup and view all the answers

What type of component is `App` in the provided code?

It is a functional component that utilizes React hooks for state management. Signup and view all the answers

What method is called to fetch user data from the API in the `useEffect`?

The <code>fetchData</code> function is called to perform the fetch operation with error handling. Signup and view all the answers

Study Notes

Ternary Operator

A shortcut for conditional statements
condition ? value1 : value2
If condition is true, returns value1; otherwise, returns value2

Switch Statement

Used for multiple conditional checks
switch (expression) evaluates the expression and matches it to the relevant case
case labels specify conditions
break statement prevents code from continuing to the next case
default case handles any unmatched conditions (optional)
Useful for handling various states

Event Listener for Window Resize

window.addEventListener("resize", function)
Executes a function when the browser window is resized
window.innerHeight, window.innerWidth get current window dimensions

State in React

useState for managing component state
State is the component's memory
Used for dynamic updates and rendering
State updates trigger re-renders

Array Manipulation in State

Editing state arrays requires updating the entire array
map method creates a new array that reflects changes
- currentUserState.map() iterates over the current array
- If currentUser.id === user.id, update the relevant values (name, email)
- ...currentUser creates a copy (critical), keeping other elements unchanged
- Important: Assign the updated array to setUser to trigger a re-render

`UserDetail` Component (with Proptypes)

Component for displaying and editing user details
user and setUser props are passed down for data interaction
useState for managing edit mode (IsEdit) and input values (name,email)
useEffect for fetching and updating user data (not in this example)

Fetch API

Asynchronous HTTP requests
fetch() inititates the request and returns a Promise
Promise chains used for handling responses (.then())
Can handle errors with .catch()
AbortController() and AbortSignal - prevent unnecessary/incomplete requests. Important when unmounting a component
Example handling of the JSONPlaceholder API

State Update with `setCounter`

useState for managing a counter
setCounter((count) => count += 1) imperative style to update the state by incrementing the current value.
useEffect triggered when sync updates. Logs the re-render to the console and updates the document title.

Post Data Example (using Fetch API for POST)

fetch for creating POST requests
Sending data as JSON to an API endpoint
setBlogData sets the new state to clear the form after a submission
Correct handling of the response including logging the data received. Also handling possible errors.

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Description

This quiz covers fundamental JavaScript concepts such as the ternary operator, switch statements, event listeners for window resizing, and managing state in React. Test your knowledge on these key topics and improve your understanding of JavaScript programming.