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?

let array = new Array(1, 2, 3); Signup and view all the answers

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

0 Signup and view all the answers

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

[ 'Black Sea', 'Caribbean Sea', 'North Sea', 'Baltic Sea', 'Red Sea' ] Signup and view all the answers

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

An element is added to the beginning Signup and view all the answers

Which statement about JavaScript arrays is false?

The size of an array is static once created. 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']?

Baltic Sea Signup and view all the answers

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

Removes the first element of the array Signup and view all the answers

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

Current element, index, and the whole array Signup and view all the answers

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

Runs a function on each item and creates a new array with the results 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?

['Hello John', 'Hello Sara', 'Hello Jack'] Signup and view all the answers

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

Returns a new array containing only items that meet a specified condition Signup and view all the answers

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

It results in a new array based on values returned by the function. Signup and view all the answers

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

To aggregate results through each iteration of the callback function Signup and view all the answers

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

It does not return anything Signup and view all the answers

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

It indicates the position of the current element being processed 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)); ?

60 Signup and view all the answers

Which scenario would best utilize the reduce() method?

Calculating the total of numbers in an array 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?

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

The initial value for the accumulator 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); ?

500 Signup and view all the answers

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

A single output value derived from the array elements 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 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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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.