JavaScript Arrays and Callbacks
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Questions and Answers

What is the primary problem associated with using multiple callbacks in asynchronous programming?

  • It reduces the number of functions needed.
  • It can lead to callback hell, impacting readability. (correct)
  • It increases the efficiency of the code.
  • It requires the use of Promises.

    • What does the Promise() constructor function require as an argument?

  • A string message to describe the promise.
  • An array of callback functions.
  • A function that contains resolve and reject methods. (correct)
  • A boolean value indicating success or failure.

    • In JavaScript asynchronous programming, what role does the resolve() function play?

  • It delays the execution of a function.
  • It terminates the execution of a function.
  • It signifies a successful completion of a promise. (correct)
  • It transforms callbacks into promises.

    • Which of the following is a potential disadvantage of using async/await in JavaScript?

    <p>It can make the code harder to understand if misused.</p> Signup and view all the answers

    What is the primary advantage of using promises over traditional callbacks?

    <p>Promises allow for chaining methods, improving readability.</p> Signup and view all the answers

    What is a callback in the context of asynchronous programming?

    <p>A function passed into another function to be executed later.</p> Signup and view all the answers

    When might it be better to use async/await instead of callbacks?

    <p>When chaining multiple asynchronous calls for maintainability.</p> Signup and view all the answers

    What does the 'reject()' function signify in a promise?

    <p>An error occurred during the promise execution.</p> Signup and view all the answers

    What does the map() method do in the context of array operations?

    <p>It creates a new array by applying a function to each element.</p> Signup and view all the answers

    Which statement accurately describes the reduce() method?

    <p>It applies a function to each element and aggregates into a single output.</p> Signup and view all the answers

    What is the purpose of the parameter 'accumulator' in the reduce() method?

    <p>It acts as a temporary storage for the intermediate results.</p> Signup and view all the answers

    What does the async keyword indicate when used before a function?

    <p>The function represents an asynchronous operation.</p> Signup and view all the answers

    Which of the following is NOT a method for array manipulation mentioned?

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

    What is the purpose of the await keyword in an async function?

    <p>To pause execution until a promise settles.</p> Signup and view all the answers

    How is the resolution of an async function presented to the caller?

    <p>It returns a promise that resolves with the function's return value.</p> Signup and view all the answers

    What does the filter() method return when provided with a function?

    <p>An array only with elements that match a certain condition.</p> Signup and view all the answers

    What happens if an error is thrown inside an async function?

    <p>The promise returned by the function rejects with that error.</p> Signup and view all the answers

    What is required to utilize the await keyword in your JavaScript code?

    <p>The function must be an async function.</p> Signup and view all the answers

    Which statement accurately defines asynchronous execution in JavaScript?

    <p>Asynchronous execution allows functions to run without waiting for previous tasks to finish.</p> Signup and view all the answers

    What result does an async function return when called?

    <p>It always returns a promise.</p> Signup and view all the answers

    What is the primary difference between Promise.all() and Promise.allSettled()?

    <p>Promise.allSettled() waits for all promises and reports their status.</p> Signup and view all the answers

    Which statement is true about handling multiple asynchronous operations with async/await?

    <p>Await does not allow parallel execution automatically.</p> Signup and view all the answers

    Study Notes

    Callback Functions

    • A callback function is a function passed as an argument to another function.
    • It's executed after the completion of some operations within the other function.
    • Callbacks allow code to respond to events or asynchronous tasks.

    JavaScript Arrays

    • JavaScript arrays can store values of mixed types.

    • Array size is dynamic, meaning it can change in size.

    • Arrays can be created using the Array constructor or array literal notation.

    • Array literal notation: let arrayName = [element1, element2, element3, ...]

    • Accessing elements: arrayName[index]

    • Finding the number of elements: arrayName.length

    Basic Array Operations

    • push(): Adds an element to the end of an array.
    • unshift(): Adds an element to the beginning of an array.
    • pop(): Removes and returns the element from the end of an array.
    • shift(): Removes and returns the element from the beginning of an array.

    forEach() array method

    • Executes a provided function once for each array element.
    • The provided function takes the element, its index, and the array itself as parameters.

    map() array method

    • Runs every item in an array through a function.
    • Returns a new array with values returned by the provided function.

    filter() array method

    • Passes each item through a defined condition.
    • Returns a new array containing the items that satisfy the condition.

    reduce() array method

    • Executes a reducer function on each element in an array.
    • Returns a single value.
    • The reducer function takes an accumulator and current value as arguments.

    Asynchronous JavaScript

    • Asynchronous operations do not execute in the order they appear in code.
    • In async programming, the program doesn't wait for tasks to complete before proceeding.
    • Tasks are often handled through the "call stack", "callback queue", "WebAPI", and "event loop" within a browser.

    Promises

    • Represent the eventual result of an asynchronous operation.
    • new Promise(function(resolve, reject)): Creates a promise object.
    • resolve(): Invoked when the operation is successful.
    • reject(): Invoked when an error occurs.
    • The then() method handles the result (or error) of a Promise.

    Asynchronous / Callback Functions

    • Callbacks pass a function to another function, expecting it to call the callback at a precise time.
    • A potential issue is "Callback Hell" in situations with multiple nested callbacks.

    Async/Await

    • Async/await simplifies asynchronous code by letting it flow sequentially.
    • async keyword for asynchronous functions.
    • Await keyword pauses execution until a Promise is resolved.

    Promise.all()

    • Takes an array of Promises as input.
    • Resolves when all input promises have resolved.
    • Returns an array of resolved values.

    Promise.allSettled()

    • Waits for all promises to settle (resolve or reject).
    • Returns an array with results for each promise, both fulfilled and rejected.

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    Related Documents

    JavaScript Array Operations PDF

    Description

    This quiz covers important concepts related to JavaScript arrays and callback functions. You'll learn about array operations, array methods like forEach, and how callbacks function as arguments in JavaScript. Test your knowledge on dynamic arrays and their manipulation.

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