Array Methods

Question 1

What parameters can be passed to the “map” method’s callback function?

Answer 1

item, index, array

Question 2

What is the format of the “map” method and what does it do?

Use multiplyByTwo as an example.

Answer 2

The “map” method creates a new array populated with the results of calling a provided function on every element in the calling array.

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const oldArr = [1, 2, 3];

  function multiplyByTwo (item, index, array) {
         return item * 2;
  }

newArr = oldArr.map(multiplyByTwo);

Question 3

List 4 array methods that return a new array

Answer 3

map, filter, reduce, slice

Question 4

What is the format of the “filter” method and what does it do?

Use idOddNumber as an example.

Answer 4

The “filter” method creates a new array with all elements that pass the test implemented by the provided function.

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const oldArr = [1, 2, 3];

  function isOddNumber(item, index, array) {
       return item % 2 !== 0;
  };

const newArr = oldArr.filter(isOddNumber);

Question 5

What is the format of the “find” method and what does it do?

Use idEqualToTen as an example.

Answer 5

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

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const myArr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14];

  function isEqualToTen(item, index, array) {
       return item === 10;
  };

const ten = oldArr.find(isEqualToTen);

Question 6

What parameters can be passed to the “filter” method’s callback function?

Answer 6

item, index, array

Question 7

What parameters can be passed to the “find” method’s callback function?

Answer 7

item, index, array

Question 8

What parameters can be passed to the “forEach” method’s callback function?

Answer 8

item, index, array

Question 9

What is the format of the “forEach” method and what does it do?

Use idEqualToTen as an example.

Answer 9

The “forEach” method executes a provided function once for each array element

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const oldArr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14];
const newArr = [];

function isEqualToTen(item, index, array) {
       if(item === 10) {
         newArr.push(item);
    }
 };

oldArr.forEach(isEqualToTen);

Question 10

What is the difference between “map” and “forEach”?

Answer 10

map returns a new array and forEach does not

Question 11

What parameters can be passed to the “every” method’s callback function?

Answer 11

item, index, array

Question 12

What is the format of the “every” method and what does it do?

Use isGreaterThanTen as an example.

Answer 12

The “every” method tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value.

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const myArr = [12, 13, 14, 27, 80];

function isGreaterThanTen(item, index, array) {
     if (item > 10) {
       return true;
    }
}

myArr.every(isGreaterThanTen);

Question 13

What parameters can be passed to the “some” method’s callback function?

Answer 13

item, index, array

Question 14

What is the format of the “some” method and what does it do?

Use isGreaterThanTen as an example.

Answer 14

The “some” method tests whether at least one element in the array passes the test implemented by the provided function. It returns a Boolean value.

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const myArr = [1, 3, 12, 13, 14, 27, 80];

function isGreaterThanTen(item, index, array) {
     if (item > 10) {
       return true;
    }
}

myArr.some(isGreaterThanTen);

Question 15

What is the format of the “reverse” method and what does it do?

Answer 15

The “reverse” method reverses and array

_________________________
const myArr = [1, 3, 12, 13, 14, 27, 80];
myArr.reverse();

Question 16

What is the format of the “includes” method and what does it do?

Answer 16

The “includes” method determines whether an array includes a certain value among its entries, returning true or false as appropriate.

_______________________
const myArr = [1, 3, 12, 13, 14, 27, 80];
myArr.includes(2);

Question 17

What parameters can be passed to the “includes” method’s callback function?

Answer 17

valueToFind, fromIndex

Question 18

List at least 8 array methods that alter an existing array

Answer 18

forEach, reverse, sort, splice, pop, push, shift, unshift

Question 19

What is the format of the “shift” method and what does it do?

Answer 19

The “shift” method removes the first element from an array and returns that removed element. This method changes the length of the array.

_______________________

Question 20

What is the format of the “unshift” method and what does it do?

Answer 20

The “unshift” method adds one or more elements to the beginning of an array and returns the new length of the array.

_______________________

Question 21

What is the difference between “shift” and “unshift”?

Answer 21

Shift removes an item from the array. Unshift adds an item to the array.

Question 22

What is the format of the “splice” method and what does it do?

Answer 22

The “splice” method changes the contents of an array by removing or replacing existing elements and/or adding new elements in place.

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const oldArr = ["maia", "matteo", "emilia", "lucia"];
const newArr = oldArr.splice("frankie",1,3);

//expect newArr = [“matteo”, “emilia”]

Question 23

What is the format of the “slice” method and what does it do?

Answer 23

The “slice” method returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included) where begin and end represent the index of items in that array. The original array will not be modified.

______________

const oldArr = ["maia", "matteo", "emilia", "lucia"];
const newArr = oldArr.slice(1,3);

//expect newArr = [“matteo”, “emilia”]

Question 24

What is the different between “map” and “filter”?

Answer 24

Map will always return an array of the same length whereas filter will return an array that contains a subset of the original array.

Question 25

What arguments can be passed to the “reduce” method’s callback function?

Answer 25

accumulator, item, index, array