JavaScript Callbacks and Arrays Quiz
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Questions and Answers

What is the primary purpose of a callback function?

  • To pass data between two functions
  • To create a new function in JavaScript
  • To store multiple values in a variable
  • To execute code in response to an event (correct)

Which method is used to add an element to the end of a JavaScript array?

  • append()
  • push() (correct)
  • add()
  • unshift()

How do you access the length of a JavaScript array?

  • Using the array length method
  • By using the count() function
  • Accessing the length property (correct)
  • Using the size property

Which of the following is a correct way to create an array in JavaScript?

<p>let array = new Array(1, 2, 3); (D)</p> Signup and view all the answers

Which index would you use to access the first element of the array 'mountains'?

<p>0 (A)</p> Signup and view all the answers

What will be the output of 'console.log(seas);' after executing seas.push('Red Sea');?

<p>[ 'Black Sea', 'Caribbean Sea', 'North Sea', 'Baltic Sea', 'Red Sea' ] (C)</p> Signup and view all the answers

What happens when you use the unshift() method on an array?

<p>An element is added to the beginning (D)</p> Signup and view all the answers

Which statement about JavaScript arrays is false?

<p>The size of an array is static once created. (D)</p> Signup and view all the answers

What will be the output of the following code: const lastElement = seas.pop(); console.log(lastElement); when seas is initialized as ['Black Sea', 'Caribbean Sea', 'North Sea', 'Baltic Sea']?

<p>Baltic Sea (D)</p> Signup and view all the answers

What does the shift() method do in an array?

<p>Removes the first element of the array (C)</p> Signup and view all the answers

What values does the forEach() method pass to its callback function when executing?

<p>Current element, index, and the whole array (A)</p> Signup and view all the answers

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

<p>Runs a function on each item and creates a new array with the results (A)</p> Signup and view all the answers

What will be the final content of the students array after executing the following code: students.forEach(myFunction); where myFunction adds 'Hello ' before each student's name?

<p>['Hello John', 'Hello Sara', 'Hello Jack'] (D)</p> Signup and view all the answers

Which of the following correctly describes the filter() method?

<p>Returns a new array containing only items that meet a specified condition (D)</p> Signup and view all the answers

Which of the following statements about the map method is true?

<p>It results in a new array based on values returned by the function. (D)</p> Signup and view all the answers

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

<p>To aggregate results through each iteration of the callback function (B)</p> Signup and view all the answers

What type of method is forEach() considered in terms of array manipulation?

<p>It does not return anything (B)</p> Signup and view all the answers

In the context of the forEach() method, what is the role of the index parameter?

<p>It indicates the position of the current element being processed (C)</p> Signup and view all the answers

What will be the output of the following code: let arr = [10, 20, 30]; console.log(arr.reduce((sum, i) => sum + i)); ?

<p>60 (A)</p> Signup and view all the answers

Which scenario would best utilize the reduce() method?

<p>Calculating the total of numbers in an array (C)</p> Signup and view all the answers

If you call a function with the forEach() method, how many times will it execute if the array has 5 elements?

<p>5 times (D)</p> Signup and view all the answers

In the use of the reduce() method, what does the second parameter represent?

<p>The initial value for the accumulator (D)</p> Signup and view all the answers

What would be logged to the console from the following code: let x=[1, 150,100].reduce((a, b) => Math.max(a, b), 500); ?

<p>500 (A)</p> Signup and view all the answers

What type of value does the reduce() method return?

<p>A single output value derived from the array elements (B)</p> Signup and view all the answers

Flashcards

Callback Function

A function that is passed as an argument to another function and is executed after some operation is completed. It's used to perform actions or provide feedback after a specific task is finished.

Callback Function - Purpose

A callback function's primary purpose is to execute code in response to an event.

JavaScript Array

A JavaScript array is a data structure that can hold values of mixed types and can dynamically change size.

JavaScript Array Creation Method 1

One way to create a JavaScript array is to use the Array constructor: 'let scores = new Array(9, 10, 8, 7, 6);'

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JavaScript Array Creation Method 2

The preferred way to create a JavaScript array is using the array literal notation: 'let arrayName = [element1, element2, element3,...];'

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Accessing Array Elements

Accessing an element in a JavaScript array is done using an index within square brackets. For example: 'let mountains = ['Everest', 'Fuji', 'Nanga Parbat']; console.log(mountains[0]); // 'Everest'

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Array Length Property

The length property of an array returns the number of elements it contains. For example: 'let mountains = ['Everest', 'Fuji', 'Nanga Parbat']; console.log(mountains.length); // 3

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Adding to the End of Array

The push() method adds an element to the end of an array.

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What does the pop() method do in JavaScript arrays?

The pop() method removes the last element from an array and returns the removed element.

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What does the shift() method do in JavaScript arrays?

The shift() method removes the first element from an array and returns the removed element.

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What does the forEach() method do in JavaScript arrays?

The forEach() method iterates over each element in an array and executes a specified function for each element.

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What is the currentValue parameter used for in the forEach() method?

The currentValue parameter represents the actual value of the current element being processed in the forEach() method.

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What does the index parameter do in the forEach() method?

The index parameter (optional) represents the numerical index of the current element in the array when using the forEach() method.

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What does the arr parameter represent in the forEach() method?

The arr parameter (optional) refers to the original array that the forEach() method is iterating over.

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What does the map() method do in JavaScript arrays?

The map() method transforms each element in an array by applying a specified function to it and returns a new array containing the transformed elements.

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What's the key difference between the map() and forEach() methods?

The map() method creates a new array, whereas the forEach() method modifies the original array in place.

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What does the map() method do?

The map() method applies a function to every element in an array and returns a new array containing the results.

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What does the filter() method do?

The filter() method creates a new array containing only the elements from the original array that meet a specified condition.

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What does the reduce() method do?

The reduce() method iterates through an array, applying a function to each element. It combines all the values into a single output.

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What are the parameters of the reduce() method's callback function?

The reduce() method's callback function takes two parameters: an accumulator and the current element of the array. The accumulator holds the accumulated result from previous iterations.

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What does the reduce() method's callback function do?

The reduce() method's callback function performs an operation on the accumulator and the current element and returns the new value of the accumulator. This value is then used in the next iteration.

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Can the reduce() method have an initial value?

The reduce() method can take an optional initial value. This value is used as the initial value of the accumulator.

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What happens if no initial value is provided to the reduce() method?

The reduce() method's accumulator is initialized to the first element of the array if no initial value is provided.

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What does the reduce() method's callback function's return value become?

In the reduce() method, the callback function's return value becomes the new accumulator value for the next iteration.

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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 main function.
  • This allows for actions to be performed based on outcomes.

JavaScript Arrays

  • JavaScript arrays can store values of different data types.
  • Array size is dynamic, meaning it can change in size.
  • Arrays can be created using the Array constructor or array literals, the latter is more common:
    • let scores = new Array(9, 10, 8, 7, 6);
  • Access elements using their index in square brackets []: let firstElement = scores[0];
  • Get the number of elements in an array using the length property: console.log(scores.length);

Basic Array Operations

  • push(): Adds an element to the end of an array: seas.push('Red Sea');

  • unshift(): Adds an element to the beginning of an array: seas.unshift('Red Sea');

  • pop(): Removes the last element from an array and returns it: const lastElement = seas.pop();

  • shift(): Removes the first element from an array and returns it: const firstElement = seas.shift();

  • forEach(): Executes a provided function once for each array element:

    • students.forEach(myFunction);
    • The function operates on each item in the array. The function is provided with the item, its index and the array itself.

  • map(): Creates a new array with the results of calling a provided function on every element in the current array.

    • let numbersDoubled = numbers.map(double);

  • filter(): Creates a new array with all elements that pass the test implemented by the provided function.

  • let highTestScores = testScores.filter(isHighScore);

  • reduce(): Executes a reducer function (that you provide) on each element of the array, resulting in a single output value.

    • console.log(arr.reduce(sumofArray));
    • The reduce function takes two parameters: an accumulator and the current value.

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JavaScript Arrays and Callback Functions PDF

Description

Test your knowledge on JavaScript callback functions and array operations with this quiz. You'll explore key concepts such as defining callback functions, manipulating arrays, and understanding basic operations. Perfect for beginners wanting to solidify their understanding of JavaScript arrays.

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