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Flashcards in Array Deck (34):
1

Array.length

var clothing = ['shoes', 'shirts', 'socks', 'sweaters'];

console.log(clothing.length);
// expected output: 4

2

Array.from()

console.log(Array.from('foo'));
// expected output: Array ["f", "o", "o"]

console.log(Array.from([1, 2, 3], x => x + x));
// expected output: Array [2, 4, 6]

3

Array.isArray()

Array.isArray([1, 2, 3]); // true
Array.isArray({foo: 123}); // false
Array.isArray('foobar'); // false
Array.isArray(undefined); // false

4

Array.of()

Array.of(7); // [7]
Array.of(1, 2, 3); // [1, 2, 3]

Array(7); // [ , , , , , , ]
Array(1, 2, 3); // [1, 2, 3]

5

Array.prototype.concat()

var array1 = ['a', 'b', 'c'];
var array2 = ['d', 'e', 'f'];

console.log(array1.concat(array2));
// expected output: Array ["a", "b", "c", "d", "e", "f"]

6

Array.prototype.copyWithin()

var array1 = [1, 2, 3, 4, 5];

// place at position 0 the element between position 3 and 4
console.log(array1.copyWithin(0, 3, 4));
// expected output: Array [4, 2, 3, 4, 5]

// place at position 1 the elements after position 3
console.log(array1.copyWithin(1, 3));
// expected output: Array [4, 4, 5, 4, 5]

7

Array.prototype.entries()

var array1 = ['a', 'b', 'c'];

var iterator1 = array1.entries();

console.log(iterator1.next().value);
// expected output: Array [0, "a"]

console.log(iterator1.next().value);
// expected output: Array [1, "b"]

8

Array.prototype.every()

function isBelowThreshold(currentValue) {
return currentValue < 40;
}

var array1 = [1, 30, 39, 29, 10, 13];

console.log(array1.every(isBelowThreshold));
// expected output: true

9

Array.prototype.fill()

var array1 = [1, 2, 3, 4];

// fill with 0 from position 2 until position 4
console.log(array1.fill(0, 2, 4));
// expected output: [1, 2, 0, 0]

// fill with 5 from position 1
console.log(array1.fill(5, 1));
// expected output: [1, 5, 5, 5]

console.log(array1.fill(6));
// expected output: [6, 6, 6, 6]

10

Array.prototype.filter()

var words = ['spray', 'limit', 'elite', 'exuberant', 'destruction', 'present'];

const result = words.filter(word => word.length > 6);

console.log(result);
// expected output: Array ["exuberant", "destruction", "present"]

11

Array.prototype.find()

var array1 = [5, 12, 8, 130, 44];

var found = array1.find(function(element) {
return element > 10;
});

console.log(found);
// expected output: 12

12

Array.prototype.findIndex()

var array1 = [5, 12, 8, 130, 44];

function findFirstLargeNumber(element) {
return element > 13;
}

console.log(array1.findIndex(findFirstLargeNumber));
// expected output: 3

13

Array.prototype.forEach()

var array1 = ['a', 'b', 'c'];

array1.forEach(function(element) {
console.log(element);
});

// expected output: "a"
// expected output: "b"
// expected output: "c"

14

Array.prototype.includes()

var array1 = [1, 2, 3];

console.log(array1.includes(2));
// expected output: true

var pets = ['cat', 'dog', 'bat'];

console.log(pets.includes('cat'));
// expected output: true

console.log(pets.includes('at'));
// expected output: false

15

Array.prototype.indexOf()

var beasts = ['ant', 'bison', 'camel', 'duck', 'bison'];

console.log(beasts.indexOf('bison'));
// expected output: 1

// start from index 2
console.log(beasts.indexOf('bison', 2));
// expected output: 4

console.log(beasts.indexOf('giraffe'));
// expected output: -1

16

Array.prototype.join()

var elements = ['Fire', 'Wind', 'Rain'];

console.log(elements.join());
// expected output: Fire,Wind,Rain

console.log(elements.join(''));
// expected output: FireWindRain

console.log(elements.join('-'));
// expected output: Fire-Wind-Rain

17

Array.prototype.keys()

var array1 = ['a', 'b', 'c'];
var iterator = array1.keys();

for (let key of iterator) {
console.log(key); // expected output: 0 1 2
}

18

Array.prototype.lastIndexOf()

var animals = ['Dodo', 'Tiger', 'Penguin', 'Dodo'];

console.log(animals.lastIndexOf('Dodo'));
// expected output: 3

console.log(animals.lastIndexOf('Tiger'));
// expected output: 1

19

Array.prototype.map()

var array1 = [1, 4, 9, 16];

// pass a function to map
const map1 = array1.map(x => x * 2);

console.log(map1);
// expected output: Array [2, 8, 18, 32]

20

Array.prototype.pop()

var plants = ['broccoli', 'cauliflower', 'cabbage', 'kale', 'tomato'];

console.log(plants.pop());
// expected output: "tomato"

console.log(plants);
// expected output: Array ["broccoli", "cauliflower", "cabbage", "kale"]

plants.pop();

console.log(plants);
// expected output: Array ["broccoli", "cauliflower", "cabbage"]

21

Array.prototype.push()

var animals = ['pigs', 'goats', 'sheep'];

console.log(animals.push('cows'));
// expected output: 4

console.log(animals);
// expected output: Array ["pigs", "goats", "sheep", "cows"]

animals.push('chickens');

console.log(animals);
// expected output: Array ["pigs", "goats", "sheep", "cows", "chickens"]

22

Array.prototype.reduce()

const array1 = [1, 2, 3, 4];
const reducer = (accumulator, currentValue) => accumulator + currentValue;

// 1 + 2 + 3 + 4
console.log(array1.reduce(reducer));
// expected output: 10

// 5 + 1 + 2 + 3 + 4
console.log(array1.reduce(reducer, 5));
// expected output: 15

23

Array.prototype.reduceRight()

const array1 = [[0, 1], [2, 3], [4, 5]].reduceRight(
(previousValue, currentValue) => previousValue.concat(currentValue)
);

console.log(array1);
// expected output: Array [4, 5, 2, 3, 0, 1]

24

Array.prototype.reverse()

var array1 = ['one', 'two', 'three'];
var reversed = array1.reverse();

console.log(array1);
// expected output: Array ['three', 'two', 'one']

console.log(reversed);
// expected output: Array ['three', 'two', 'one']

25

Array.prototype.shift()

var array1 = [1, 2, 3];

var firstElement = array1.shift();

console.log(array1);
// expected output: Array [2, 3]

console.log(firstElement);
// expected output: 1

26

Array.prototype.slice()

var animals = ['ant', 'bison', 'camel', 'duck', 'elephant'];

console.log(animals.slice(2));
// expected output: Array ["camel", "duck", "elephant"]

console.log(animals.slice(2, 4));
// expected output: Array ["camel", "duck"]

console.log(animals.slice(1, 5));
// expected output: Array ["bison", "camel", "duck", "elephant"]

27

Array.prototype.some()

var array = [1, 2, 3, 4, 5];

var even = function(element) {
// checks whether an element is even
return element % 2 === 0;
};

console.log(array.some(even));
// expected output: true

28

Array.prototype.sort()

var months = ['March', 'Jan', 'Feb', 'Dec'];
months.sort();
console.log(months);
// expected output: Array ["Dec", "Feb", "Jan", "March"]

var array1 = [1, 30, 4, 21];
array1.sort();
console.log(array1);
// expected output: Array [1, 21, 30, 4]

29

Array.prototype.splice()

var months = ['Jan', 'March', 'April', 'June'];
months.splice(1, 0, 'Feb');
// inserts at 1st index position
console.log(months);
// expected output: Array ['Jan', 'Feb', 'March', 'April', 'June']

months.splice(4, 1, 'May');
// replaces 1 element at 4th index
console.log(months);
// expected output: Array ['Jan', 'Feb', 'March', 'April', 'May']

30

Array.prototype.toLocaleString()

var array1 = [1, 'a', new Date('21 Dec 1997 14:12:00 UTC')];
var localeString = array1.toLocaleString('en', {timeZone: "UTC"});

console.log(localeString);
// expected output: "1,a,12/21/1997, 2:12:00 PM",
// This assumes "en" locale and UTC timezone - your results may vary

31

Array.prototype.toSource()

var alpha = new Array('a', 'b', 'c');

alpha.toSource();
//returns ['a', 'b', 'c']

32

Array.prototype.toString()

var array1 = [1, 2, 'a', '1a'];

console.log(array1.toString());
// expected output: "1,2,a,1a"

33

Array.prototype.unshift()

var array1 = [1, 2, 3];

console.log(array1.unshift(4, 5));
// expected output: 5

console.log(array1);
// expected output: Array [4, 5, 1, 2, 3]

34

Array.prototype.values()

const array1 = ['a', 'b', 'c'];
const iterator = array1.values();

for (const value of iterator) {
console.log(value); // expected output: "a" "b" "c"
}