JS Arrays

Question 1

array1.concat(array2, array3, …, arrayX)

Answer 1

Returns Array. Joins two or more arrays, and returns a copy of the joined arrays

Question 2

array.copyWithin(target, ?start, ?end)

target: The index position to copy the elements to
start: The index position to start copying elements from (default is 0)
end: The index position to stop copying elements from (default is array.length)

Answer 2

Returns modified Array. Copies array elements within the array, to and from specified positions

Question 3

array.every(function(currentValue, ?index, ?arr), ?thisValue)

Function arguments:
currentValue: The value of the current element
index: The array index of the current element
arr: The array object the current element belongs to

thisValue: A value to be passed to the function to be used as its “this” value.
If this parameter is empty, the value “undefined” will be passed as its “this” value

Answer 3

Returns Boolean. Checks if every element in an array pass a test

Question 4

array.fill(value, start, end)

Answer 4

Returns modified Array. Fill the elements in an array with a static value

Question 5

array.filter(function(currentValue, index, arr), thisValue)

Function arguments:
currentValue: The value of the current element
index: The array index of the current element
arr: The array object the current element belongs to

thisValue: A value to be passed to the function to be used as its “this” value.
If this parameter is empty, the value “undefined” will be passed as its “this” value

Answer 5

Returns new Array. Creates a new array with every element in an array that pass a test

Question 6

array.find(function(currentValue, index, arr),thisValue)

Function arguments:
currentValue: The value of the current element
index: The array index of the current element
arr: The array object the current element belongs to

thisValue: A value to be passed to the function to be used as its “this” value.
If this parameter is empty, the value “undefined” will be passed as its “this” value

Answer 6

Returns the value of the first element in an array that pass a test; returns undefined is none pass

Question 7

array.findIndex(function(currentValue, index, arr), thisValue)

Function arguments:
currentValue: The value of the current element
index: The array index of the current element
arr: The array object the current element belongs to

thisValue: A value to be passed to the function to be used as its “this” value.
If this parameter is empty, the value “undefined” will be passed as its “this” value

Answer 7

Returns the index of the first element in an array that pass a test; if none, returns -1

Question 8

array.forEach(function(currentValue, index, arr), thisValue)

Function arguments:
currentValue: The value of the current element
index: The array index of the current element
arr: The array object the current element belongs to

thisValue: A value to be passed to the function to be used as its “this” value.
If this parameter is empty, the value “undefined” will be passed as its “this” value

Answer 8

Calls a function for each array element

Question 9

array.indexOf(item, ?start)

if start negative will count from end and continue to end

Answer 9

Search the array for an element and returns its position

Question 10

Array.isArray(obj)

Answer 10

Return Boolean. Checks whether an object is an array

Question 11

array.join(?separator)

if no separator, defaults to comma

Answer 11

Returns String. Joins all elements of an array into a string

Question 12

array. lastIndexOf(item, ?start)
start: Where to start the search. Negative values will start at the given position counting from the end, and search to the beginning

Answer 12

Search the array for an element, starting at the end, and returns its position

Question 13

array.map(function(currentValue, index, arr), thisValue)

Function arguments:
currentValue: The value of the current element
index: The array index of the current element
arr: The array object the current element belongs to

thisValue: A value to be passed to the function to be used as its “this” value.
If this parameter is empty, the value “undefined” will be passed as its “this” value

Answer 13

Returns new Array. Creates a new array with the result of calling a function for each array element

Question 14

array.pop()

Answer 14

Removes the last element of an array, and returns that element, changes original array

Question 15

array.push(item1, item2, …, itemX)

Answer 15

Adds new elements to the end of an array, and returns the new length

Question 16

array.reduce(function(total, currentValue, currentIndex, arr), ?initialValue)

Function arguments:
total: The initialValue, or the previously returned value of the function
currentValue: The value of the current element
index: The array index of the current element
arr: The array object the current element belongs to

initialValue: A value to be passed to the function as the initial value

Answer 16

Reduce the values of an array to a single value (going left-to-right), Returns the accumulated result from the last call of the callback function

Question 17

array.reduceRight(function(total, currentValue, currentIndex, arr), initialValue)

Function arguments:
total: The initialValue, or the previously returned value of the function
currentValue: The value of the current element
index: The array index of the current element
arr: The array object the current element belongs to

initialValue: A value to be passed to the function as the initial value

Answer 17

Reduce the values of an array to a single value (going right-to-left), Returns the accumulated result from the last call of the callback function

Question 18

array.reverse()

Answer 18

Returns modified array. Reverses the order of the elements in an array

Question 19

array.shift()

Answer 19

Removes the first element of an array, and returns that element, changes original array

Question 20

array. slice(?start, ?end)
start: An integer that specifies where to start the selection (The first element has an index of 0). Use negative numbers to select from the end of an array. If omitted, it acts like “0”
end: An integer that specifies where to end the selection. If omitted, all elements from the start position and to the end of the array will be selected. Use negative numbers to select from the end of an array

Answer 20

Selects a part of an array, and returns the new array

Question 21

array.some(function(currentValue, index, arr), thisValue)

Function arguments:
currentValue: The value of the current element
index: The array index of the current element
arr: The array object the current element belongs to

thisValue: A value to be passed to the function to be used as its “this” value.
If this parameter is empty, the value “undefined” will be passed as its “this” value

Answer 21

Returns Boolean. Checks if any of the elements in an array pass a test

Question 22

array.sort(?compareFunction)

Default sorts as strings alphabetically

compareFunction: A function that defines an alternative sort order. The function should return a negative, zero, or positive value, depending on the arguments, like:
function(a, b){return a-b}
When the sort() method compares two values, it sends the values to the compare function, and sorts the values according to the returned (negative, zero, positive) value.

Ex. var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a-b});

Answer 22

Returns modified array. Sorts the elements of an array

Question 23

array.splice(index, ?howmany, ?item1, ….., itemX)

index: An integer that specifies at what position to add/remove items, Use negative values to specify the position from the end of the array
howmany: The number of items to be removed. If set to 0, no items will be removed
item1, …, itemX: The new item(s) to be added to the array

Ex.
var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 1, "Lemon", "Kiwi");
The result of fruits will be:
Banana,Orange,Lemon,Kiwi,Mango

Answer 23

Returns a new Array, containing the removed items (if any). Modifies original array. Adds/Removes elements from an array

Question 24

array.toString()

Answer 24

Converts an array to a string, and returns the result

Question 25

array.unshift(item1, item2, …, itemX)

Answer 25

Adds new elements to the beginning of an array, and returns the new length

Question 26

array.valueOf()

Answer 26

Returns the primitive value of an array