JavaScript Array Methods

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Questions and Answers

Which of the following statements accurately distinguishes the `push()` and `pop()` methods from the `shift()` and `unshift()` methods in JavaScript arrays?

`push()` and `shift()` add elements, while `pop()` and `unshift()` remove elements, regardless of position.
`push()` and `unshift()` add elements to the end, while `pop()` and `shift()` remove elements from the beginning.
`push()` and `pop()` add/remove elements from the end of the array, while `shift()` and `unshift()` add/remove elements from the beginning. (correct)
`push()` and `pop()` add/remove elements from the beginning of the array, while `shift()` and `unshift()` add/remove elements from the end.

What is the purpose of the `numb` parameter in the `splice()` method, and how does its value affect the array?

It specifies the index at which to start inserting new elements. If it's 0, no elements are added.
It indicates the total number of elements that should remain in the array after the `splice()` operation. Elements are either added or removed to achieve this count.
It determines the number of elements to remove starting from the position defined by `pos`. A value of 0 means no elements are removed. (correct)
It sets a limit on the number of `itemX` parameters that can be inserted into the array. Excess parameters are ignored.

In the context of the `splice()` method, what occurs when the `itemX` parameters are provided after `pos` and `numb`?

The `itemX` parameters are appended to the end of the array, after the splice operation is complete.
The `itemX` parameters are inserted into the array at the position specified by `pos`. Existing elements at `pos` and beyond shift to the right to accommodate the new elements. (correct)
The `itemX` parameters replace the elements being removed, one-to-one, based on their order.
The `itemX` parameters are ignored because they are only relevant when removing elements from the array.

Which array methods modify the original array?

<code>push()</code> (B) Signup and view all the answers

Given an array `myArray = [10, 20, 30, 40, 50]`, what will `myArray` be after calling `myArray.splice(2, 1, 35)`?

[10, 20, 35, 40, 50] (C) Signup and view all the answers

When searching an array using `indexOf()`, what is a limitation compared to `findIndex()`?

It cannot focus on properties of the string elements. (B) Signup and view all the answers

If `arr = [1, 2, 3, 4, 5]`, what does `arr.slice(1, 4)` return?

[2, 3, 4] (A) Signup and view all the answers

Which of these methods adds an element to the beginning of an array?

<code>unshift()</code> (B) Signup and view all the answers

You have an array of `Book` objects and need to find the first book written by a specific author. Which method is most suitable?

<code>findIndex()</code> (C) Signup and view all the answers

What is the primary purpose of the `filter()` method?

To return all elements that satisfy a condition defined by a callback function. (D) Signup and view all the answers

What is the primary difference between the `slice()` method and the `splice()` method on Javascript arrays?

<code>slice()</code> creates a new array based on a portion of an existing array; <code>splice()</code> modifies the content of an existing array. (A) Signup and view all the answers

How does the return value of `filter()` differ from `findIndex()`?

<code>filter()</code> returns an array of all matching elements, while <code>findIndex()</code> returns the index of the first matching element. (A) Signup and view all the answers

What does the `map()` method do to each element of an array?

It transforms each element into a new element based on a provided function. (C) Signup and view all the answers

What is the return value of the `map()` method?

A new array with each element being the result of the callback function. (D) Signup and view all the answers

Consider an array of `Student` objects. How could you use the `map()` method to create an array containing only the first names of the students?

By providing a callback function that returns the <code>firstName</code> property of each <code>Student</code> object. (D) Signup and view all the answers

Given an array of `Game` objects, how would you use `map()` to create a simplified array of strings representing the outcome of each game ('win', 'loss', 'tie', or 'not yet')?

Apply <code>map()</code> with a callback function that checks the game's outcome and returns the corresponding string. (C) Signup and view all the answers

What is the primary function of the `slice()` method when applied to an array?

To return a new array containing a portion of the original array. (C) Signup and view all the answers

How does the `slice()` method handle the element at the `end` position?

It excludes the element at the <code>end</code> position from the new sub-array. (D) Signup and view all the answers

What does the `item` parameter represent in the `indexOf()`, `lastIndexOf()`, and `includes()` methods?

The specific value to search for within the array. (B) Signup and view all the answers

If the `item` is not found within the array, what do the `indexOf()` and `lastIndexOf()` methods return?

-1 (D) Signup and view all the answers

How does the optional `startPos` parameter in `indexOf()`, `lastIndexOf()`, and `includes()` methods affect the search?

It sets the index from which the search begins. (D) Signup and view all the answers

What is a key distinction between using a loop with `indexOf()` and using the `filter()` method for finding multiple matches in an array?

<code>indexOf()</code> only returns the index of the first match, requiring a loop to find subsequent matches, whereas <code>filter()</code> returns all matches in a new array. (B) Signup and view all the answers

In the context of JavaScript, what is a callback function?

A function that is passed as an argument to another function, to be executed at a later point. (A) Signup and view all the answers

Why are callback functions useful in designing flexible and modular code?

They allow functions to be generalized, adapting behavior based on the specific callback provided. (D) Signup and view all the answers

In the `doSomethingMathy` function, what is the purpose of the `displayFunction` parameter?

To display the calculated value after the mathematical operations. (C) Signup and view all the answers

Which of the following is a valid way to call the `doSomethingMathy` function, assuming `useAnAlert`, `useHTML`, and `useTheConsole` are defined as in the content?

<code>doSomethingMathy(50, useAnAlert)</code> (B) Signup and view all the answers

What is the primary difference between `indexOf()` and `findIndex()` methods when searching an array?

<code>indexOf()</code> searches for a specific value, while <code>findIndex()</code> uses a callback function to define a search condition. (C) Signup and view all the answers

Why might `findIndex()` be more suitable than `indexOf()` when searching for an object within an array of objects?

<code>indexOf()</code> only compares object references, while <code>findIndex()</code> can compare object properties. (D) Signup and view all the answers

Consider an array of objects, each with 'name' and 'age' properties. Which of the following `findIndex()` calls correctly finds the index of the first object with an age greater than 25?

<code>array.findIndex(item => item.age > 25)</code> (C) Signup and view all the answers

What is the primary purpose of `findLastIndex()`?

To find the index of the last element that satisfies a condition defined by a callback function. (C) Signup and view all the answers

Given an array `myArray = [{name: 'Alice', id: 1}, {name: 'Bob', id: 2}, {name: 'Alice', id: 3}]`, which method would be most efficient to find the index of the last object with the name 'Alice'?

<code>myArray.findLastIndex(obj => obj.name === 'Alice')</code> (B) Signup and view all the answers

In what scenario would using `find()` be more appropriate than using `findIndex()`?

When you only need to retrieve the first element that matches a condition, not its index. (D) Signup and view all the answers

Given an array of objects, what is the expected outcome if the `sort()` method is called without a callback function and the objects lack a custom `toString()` method?

The array will be sorted based on the default <code>toString()</code> representation, resulting in a consistent but likely unsorted order. (D) Signup and view all the answers

What is the consequence of sorting an array of strings using the `sort()` method without a callback function, considering the default alphabetical sorting?

Strings will be sorted alphabetically, but uppercase letters will precede lowercase letters. (A) Signup and view all the answers

In the context of the `sort()` method, what do the two parameters passed to the callback function represent?

Two elements from the array being compared to determine their relative order. (D) Signup and view all the answers

How does the `sort()` method utilize the callback function to determine the order of elements within an array?

The <code>sort()</code> method uses the callback function to compare pairs of elements, shuffling their positions until the array is fully sorted. (A) Signup and view all the answers

Which of the following code snippets correctly uses the `forEach()` method to print only the even numbers from an array of integers?

<code>numbers.forEach(num => { if (num % 2 === 0) { console.log(num); } });</code> (A) Signup and view all the answers

Given an array of mixed-case strings, how can you sort them alphabetically in a case-insensitive manner using the `sort()` method?

Use <code>array.sort((a, b) => a.toLowerCase().localeCompare(b.toLowerCase()))</code>. (D) Signup and view all the answers

What is the purpose of the `map()` method when transforming an array of one type (e.g., `Blah`) into an array of another type (e.g., `Foo`)?

To apply a transformation function to each element, creating a new array with the transformed elements. (A) Signup and view all the answers

Consider an array of objects with a numeric `age` property. How would you sort this array in descending order based on the `age` property?

<code>array.sort((a, b) => b.age - a.age)</code> (B) Signup and view all the answers

What order does `list.sort( (a, b) => b.price - a.price )` sort a list of products by price?

Descending order (D) Signup and view all the answers

Given `let list1 = [3, -2, 5]`, what is the result of `let list2 = list1.map( (a) => a*a )`?

[9, 4, 25] (A) Signup and view all the answers

Given `let list1 = [ "a", "happy", "nope", "whatever" ]`, what is the result of the following code?

`let list2 = list1.map( (a) => { if( a.length < 5 ) return "short"; else return a; });`

["short", "happy", "short", "whatever"] (B) Signup and view all the answers

What does the following code do?

`let list1 = //some list of products on our website let list2 = list1.filter( (a) => a.price < 100 )`

Creates a new list (list2) containing only the elements from list1 where the price is less than 100. (C) Signup and view all the answers

What data type will `foo` be after running the following code?

`let list = //some list of products on our website...assume that they have a price property let foo = list.reduce( (acc, item) => { if(acc.price > item.price) return acc; else return item; });`

Product (D) Signup and view all the answers

What does the optional second parameter in the `reduce()` method represent?

The initial value of the accumulator (B) Signup and view all the answers

What happens if you do not provide a starting value to the `reduce()` method?

The accumulator starts with the first element of the list, and the item parameter starts with the second element. (C) Signup and view all the answers

You have list of objects, each with a `date` property represented as a string `'YYYY-MM-DD'`. How would you sort this list in chronological order (oldest to newest)?

<code>list.sort((a, b) => new Date(a.date) - new Date(b.date))</code> (A) Signup and view all the answers

Flashcards

What does push() do?

Adds elements to the end of an array.

What does pop() do?

Removes and returns the last element of an array.