Array Methods

Question 1

some()

Answer 1

tests if at least one element in the array passes the test implemented by the provided function.

Arrow Function example.

    arr. some( x => x > 10)
    arr. some(x => val === x

Question 2

concat()

Answer 2

returns a new array by merging two or more values/arrays.

Question 3

filter()

Answer 3

return array with all elements that passed the test defined by the given function.
Does not change the original array.

filter() calls a provided callbackFn function once for each element in an array and constructs a new array of all the values for which callbackFn returns a value that coerces to true.

Question 4

forEach()

Answer 4

executes a provided function once for each array element.

Does not change the original array.
Does not return anything
only using data

Question 5

map()

Answer 5

executes a provided function once for each array element.It builds a new Array.

does not change the original array.

Question 6

reduce()

Answer 6

The reduce() method executes a reducer function (that you provide) on each element of the array, resulting in a single output value.

(accumulator, currentValue) => accumulator + currentValue;

Question 7

pop()

Answer 7

remove last item

Question 8

shift()

Answer 8

remove first item

Question 9

push()

Answer 9

add item to the end

Question 10

unshift()

Answer 10

add item to the front

Question 11

splice()

Answer 11

removes array items and replaces new items if provided

first start
second how many remove including start
we can use negative numbers.

Question 12

slice()

Answer 12

returns a new array containing the specified items except the last index provided.

slice(beginning, end)
Does not modify existing array
Returns a new array

Question 13

indexOf()

Answer 13

The indexOf() method returns the first index at which a given element can be found in the array, or -1 if it is not present.

Can be used to check if element is present in the array/

if ( arr.indexOf > -1) {}

Question 14

lastIndexOf()

Answer 14

returns the last occurrence of the element your searching

return the index of element.

Question 15

includes()

Answer 15

This method checks if an item is present in the array and returns a Boolean.

Question 16

find()

Answer 16

The find() method returns the value of the first element in the provided array that satisfies the provided testing function.

The find method executes the callbackFn function once for each index of the array until the callbackFn returns a truthy value. If so, find immediately returns the value of that element. Otherwise, find returns undefined.

Question 17

findIndexOf()

Answer 17

the findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise, it returns -1, indicating that no element passed the test.

Question 18

sort()

Answer 18

The sort() method sorts the elements of an array in place and returns the sorted array. The default sort order is ascending.

Question 19

every()

Answer 19

every method tests whether all elements in the array pass the test implemented by the provided function

returns a boolean.

Question 20

some()

Answer 20

some method tests whether at least one element in the array pass the test implemented by the provided function.

returns a boolean.

Question 21

Key in objects

Answer 21

A key is like a variable name that points to a location in memory that holds a value.

Question 22

JavaScript object literal

Answer 22

JavaScript object literal is a comma-separated list of name-value pairs wrapped in curly braces. Object literals encapsulate data, enclosing it in a tidy package.

Question 23

this

Answer 23

THIS keyword references the calling object which provides access to the calling object’s properties.

The reserved keyword this refers to a method’s calling object, and it can be used to access properties belonging to that object.

Question 24

getters

Answer 24

access properties in objects

Question 25

setters

Answer 25

change properties in objects. need at least one paramenter

Question 26

factory function

Answer 26

returns objects.

Question 27

Object.key()

Answer 27

Returns array key names

Question 28

Object.entries()

Answer 28

Returns array of key-value pairs. Lets us loop over objects easily.

Question 29

Object.assign()

Answer 29

merge objects together.

Question 30

Object.values()

Answer 30

Returns values of objects.

Question 31

Objects Data Type

Answer 31

An object is a built-in data type for storing key-value pairs. Data inside objects are unordered, and the values can be of any type.

Question 32

Array Data Type

Answer 32

Arrays let us gather data items into an ordered list.

Question 33

for in loops

Answer 33

Itereate over keys of an object.

Question 34

callback function

Answer 34

a function passed into another f as an argument.