6. JavaScript Array

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Questions and Answers

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

Merges two arrays into one

Returns the last element removed from the array (correct)

Adds an element to the end of the array

Removes the first element from the array

What will the output of console.log(fruits.toString()) be after executing the following code: let fruits = ['Apple', 'Banana', 'Pear']; fruits.pop(); ?

'Apple,Banana' (correct)

'Apple,Banana,Pear'

'Banana,Pear'

'Apple,Pear'

What is the effect of using unshift() on an array?

It sorts the array in ascending order

It removes elements from the end of the array

It returns the new length of the array and modifies the existing array (correct)

It creates a copy of the array

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

It returns a new array without altering the original arrays Signup and view all the answers

What will console.log(num.shift()) return given the array let num = [1, 2, 3];?

1 Signup and view all the answers

What starting index number is used to access elements in an array?

0 Signup and view all the answers

What does the length property of an array represent?

The total count of the elements in the array Signup and view all the answers

What will be the output of console.log(fruits.toString()) for the array let fruits = ['Apple', 'Banana', 'Pear']?

Apple,Banana,Pear Signup and view all the answers

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

Removes the last element from the array Signup and view all the answers

If you want to concatenate all elements of an array into a string with a custom separator, which method would you use?

join() Signup and view all the answers

What will be the result of array = array + array when array is initialized as array = 1?

3 Signup and view all the answers

Which of the following statements about the shift() and unshift() methods is correct?

shift() removes the first element, unshift() adds to the beginning Signup and view all the answers

Given the array let mix = [1, 'Apple', 22, 'Banana'], what does console.log(mix[mix.length-3]) output?

Apple Signup and view all the answers

What will the variable 'result1' contain after executing the filter function on the array 'words'?

Words with lengths greater than 6 Signup and view all the answers

Which statement correctly describes why the 'fakeSheeps' variable equals 'sheeps'?

It assigns the same reference of the array. Signup and view all the answers

What is one way to create a proper copy of the array 'array'?

let arrayCopy2 = Array.from(array); Signup and view all the answers

Which of the following methods is NOT mentioned as an array method in the content?

reduce() Signup and view all the answers

How can the rest parameters be defined in a function?

By declaring a single parameter with a spread operator. Signup and view all the answers

What is the outcome of the expression 'sheeps === cloneSheeps'?

It will return false, indicating they are different objects. Signup and view all the answers

What does the map method do when it processes each element?

It returns a new array with the results of calling a provided function on every element. Signup and view all the answers

In the context of array copying, what is a drawback of the 'bad' copying method illustrated?

It copies the reference rather than the values. Signup and view all the answers

What is the resulting array after executing num.unshift(22, 33) on the array let num = [1, 2, 3];?

[22, 33, 2, 3] Signup and view all the answers

Which of the following statements about the concat() method is true?

concat() returns a new array containing merged elements. Signup and view all the answers

What will console.log(fruits.length) output after executing the following code: let fruits = ['Apple', 'Banana', 'Pear']; fruits.pop(); ?

2 Signup and view all the answers

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

It creates a new array with elements that pass a specific test. Signup and view all the answers

Given the array let array = ['abc', true, 1, 99, false]; what will the following loop print out? for (let i = 0; i < array.length; i++) { console.log(array[i]); }

Each element of the array on a new line Signup and view all the answers

What will be the result of calling array.length when array has been populated with elements?

The total count of elements in the array Signup and view all the answers

Which method would you use to convert an array into a single string with a specified separator?

join() Signup and view all the answers

What does the pop() method return when applied to an array?

The last element of the array and modifies the array length Signup and view all the answers

What is the effect of using the push() method on an array?

It adds one or more elements to the end of the array Signup and view all the answers

In the array 'fruits = ["Apple", "Banana", "Pear"]', what will console.log(fruits.join(" *** ")) output?

"Apple *** Banana *** Pear" Signup and view all the answers

What is the initial value of array elements when declared with 'let arr = []'?

Undefined Signup and view all the answers

Which of the following statements correctly describes the toString() method?

It returns a string representation of the specified array and its elements. Signup and view all the answers

What will be contained in the 'result1' variable after executing the filter function on the array 'words'?

All words with more than 6 characters Signup and view all the answers

What will console.log(mix[mix.length-3]) return for mix = [1, 'Apple', 22, 'Banana']?

1 Signup and view all the answers

What does the spread operator '...' do when used with the 'sheeps' array?

It creates a shallow copy of the array Signup and view all the answers

Which statement correctly describes the difference between 'fakeSheeps' and 'cloneSheeps' variables?

'cloneSheeps' points to the same memory space, 'fakeSheeps' does not Signup and view all the answers

Which method is used to check if all elements in an array meet a certain condition?

every() Signup and view all the answers

What mistake is made in the 'bad' copying practice illustrated in the content?

Creating a reference instead of a copy Signup and view all the answers

How is the 'map()' function used incorrectly in the 'bad' example?

The function's syntax does not use arrow functions Signup and view all the answers

What is the purpose of a callback function when using the 'filter()' method?

To determine if elements meet a certain condition Signup and view all the answers

What does the rest parameter syntax allow in a function definition?

To group multiple arguments into an array Signup and view all the answers

Study Notes

Arrays

Arrays are data structures holding elements.
Array elements are numbered, starting from zero.
Access elements using their number in square brackets.
The total count of array elements is its length.
The toString() method returns a string representation of the array and its elements.
The join() method concatenates array elements, separated by commas or a specified separator string.

Array Methods

pop(): Removes and returns the last element of an array. Changes the array's length.
push(): Adds one or more elements to the end of an array, and returns the new length.
shift(): Removes and returns the first element of an array. Changes the array's length.
unshift(): Adds one or more elements to the beginning of an array and returns the new length.
concat(): Merges two or more arrays into a new array, without altering the original arrays.
forEach(): Executes a provided function once for each array element.
map(): Creates a new array with the results of calling a provided function on every element.
filter(): Creates a new array with all elements that pass a provided test.

Other Methods

find(), every(), some(), includes() - Additional array methods.

Arrays Copy

Arrays in JavaScript are reference values, meaning when you copy an array using = you copy the reference, not the array contents. Modifying one copy will also modify the original.
To create a true copy, use spread syntax (...) or other methods that explicitly copy the array elements.

Best Practices

Use of for...in and for...of loops are less efficient than forEach function.
Use rest parameters (...) to accept an indefinite number of arguments in a function as an array.
Spread syntax can expand iterables like arrays into their elements (for function calls or as new variables).

Sorting Arrays

sort() may not sort in a way you expect it to work with numbers unless a comparison function is supplied specifically
Avoid using array.sort() with numbers if unexpected results are required with the elements of an array, or it is essential which sorting behavior to achieve.

Studying That Suits You

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This quiz covers the basics of arrays, including their structure and key methods like pop(), push(), and concat(). Test your understanding of how to manipulate and access array elements effectively in programming. Ideal for students learning about data structures.

6. JavaScript Array

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Questions and Answers

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

What will the output of console.log(fruits.toString()) be after executing the following code: let fruits = ['Apple', 'Banana', 'Pear']; fruits.pop(); ?

What is the effect of using unshift() on an array?

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

What will console.log(num.shift()) return given the array let num = [1, 2, 3];?

What starting index number is used to access elements in an array?

What does the length property of an array represent?

What will be the output of console.log(fruits.toString()) for the array let fruits = ['Apple', 'Banana', 'Pear']?

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

If you want to concatenate all elements of an array into a string with a custom separator, which method would you use?

What will be the result of array = array + array when array is initialized as array = 1?

Which of the following statements about the shift() and unshift() methods is correct?

Given the array let mix = [1, 'Apple', 22, 'Banana'], what does console.log(mix[mix.length-3]) output?

What will the variable 'result1' contain after executing the filter function on the array 'words'?

Which statement correctly describes why the 'fakeSheeps' variable equals 'sheeps'?

What is one way to create a proper copy of the array 'array'?

Which of the following methods is NOT mentioned as an array method in the content?

How can the rest parameters be defined in a function?

What is the outcome of the expression 'sheeps === cloneSheeps'?

What does the map method do when it processes each element?

In the context of array copying, what is a drawback of the 'bad' copying method illustrated?

What is the resulting array after executing num.unshift(22, 33) on the array let num = [1, 2, 3];?

Which of the following statements about the concat() method is true?

What will console.log(fruits.length) output after executing the following code: let fruits = ['Apple', 'Banana', 'Pear']; fruits.pop(); ?

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

Given the array let array = ['abc', true, 1, 99, false]; what will the following loop print out? for (let i = 0; i < array.length; i++) { console.log(array[i]); }

What will be the result of calling array.length when array has been populated with elements?

Which method would you use to convert an array into a single string with a specified separator?

What does the pop() method return when applied to an array?

What is the effect of using the push() method on an array?

In the array 'fruits = ["Apple", "Banana", "Pear"]', what will console.log(fruits.join(" *** ")) output?

What is the initial value of array elements when declared with 'let arr = []'?

Which of the following statements correctly describes the toString() method?

What will be contained in the 'result1' variable after executing the filter function on the array 'words'?

What will console.log(mix[mix.length-3]) return for mix = [1, 'Apple', 22, 'Banana']?

What does the spread operator '...' do when used with the 'sheeps' array?

Which statement correctly describes the difference between 'fakeSheeps' and 'cloneSheeps' variables?

Which method is used to check if all elements in an array meet a certain condition?

What mistake is made in the 'bad' copying practice illustrated in the content?

How is the 'map()' function used incorrectly in the 'bad' example?

What is the purpose of a callback function when using the 'filter()' method?

What does the rest parameter syntax allow in a function definition?

Study Notes

Arrays

Array Methods

Other Methods

Arrays Copy

Best Practices

Sorting Arrays

Studying That Suits You

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