JavaScript Array Reference #2 – Quick Learn

Array reference JavaScript quick learning series part 2

1-) keys()

The keys() method returns an Array Iterator object with the keys of an array.

const fruits = ["Muz", "Portakal", "Elma", "kiwi"];
const keys = fruits.keys();

for (let x of keys) {
  console.log(x);
}

OUTPUT:

0

1

2

3

2-) lastIndexOf()

The lastIndexOf() method returns the last index (position) of a specified value.

const fruits = ["Armut", "Muz", "Kiwi", "Çilek"];
let index = fruits.lastIndexOf("Kiwi");

console.log(index);

OUTPUT : 2

3-) length

The length property sets or returns the number of elements in an array.

const fruits = ["Muz", "Kiwi", "Elma", "Çilek"];
let length = fruits.length;

console.log(length);

OUTPUT : 4

4-) map()

map() creates a new array from calling a function for every array element.

const numbers = [4, 9, 16, 25];
const newArr = numbers.map(Math.sqrt)

console.log(newArr);

OUTPUT : 2,3,4,5

5-) pop()

The pop() method removes (pops) the last element of an array.

const fruits = ["Elma", "Armut", "Portakal", "Muz"];


console.log(fruits.pop());

OUTPUT : Elma,Armut,Portakal

6-) prototype

prototype allows you to add new properties and methods to arrays.

prototype is a property available with all JavaScript objects.

// Add a new method
Array.prototype.myUcase = function() {
  for (let i = 0; i < this.length; i++) {
    this[i] = this[i].toUpperCase();
  }
};

// Use the method on any array
const fruits = ["Elma", "Armut", "Portakal", "Kiwi"];


 console.log(fruits.myUcase());

OUTPUT : ELMA,ARMUT,PORTAKAL,KIWI

7-) push()

The push() method adds new items to the end of an array.

The push() method changes the length of the array.

const fruits = ["Elma", "Armut", "Portakal", "Muz"];


console.log(fruits.push("Kiwi"));

OUTPUT : Elma,Armut,Portakal,Muz,Kiwi

8-) reduce()

The reduce() method executes a reducer function for array element.

The reduce() method returns a single value: the function's accumulated result.

const numbers = [175, 50, 25];

console.log(numbers.reduce(myFunc));

function myFunc(total, num) {
  return total - num;
}

OUTPUT: 100

9-) reduceRight()

The reduceRight() method executes a reducer function for each array element.

The reduceRight() method works from right to left.

const numbers = [175, 50, 25];

console.log(numbers.reduceRight(myFunc));

function myFunc(total, num) {
  return total - num;
}

OUTPUT: -200

10-) reverse()

The reverse() method reverses the order of the elements in an array.

The reverse() method overwrites the original array.

const fruits = ["Elma", "Armut", "Muz", "Kiwi"];
fruits.reverse();

console.log(fruits.reverse());

OUTPUT: Kiwi,Armut,Muz,Kiwi

11-) shift()

The shift() method removes the first item of an array.

The shift() method changes the original array.

const fruits = ["Elma", "Armut", "Muz", "Kiwi"];
fruits.shift();

console.log(fruits);

OUTPUT: Armut,Muz,Kiwi

12-) slice()

The slice() method returns selected elements in an array, as a new array.

The slice() method selects from a given start, up to a (not inclusive) given end.

const fruits = ["Elma", "Armut", "Portakal", "Limon", "Muz"];
const citrus = fruits.slice(1, 3);

console.log(citrus);

OUTPUT: Armut,Portakal

13-) some()

The some() method checks if any array elements pass a test (provided as a callback function).

The some() method executes the callback function once for each array element.

const ages = [3, 10, 18, 20];

console.log(ages.some(checkAdult));

ages.some(checkAdult);
function checkAdult(age) {
  return age > 18;
}

OUTPUT: true

14-) sort()

The sort() sorts the elements of an array.

The sort() overwrites the original array.

The sort() sorts the elements as strings in alphabetical and ascending order.

const fruits = ["Elma", "Armut", "Muz", "Kiwi"];
console.log(fruits.sort());

OUTPUT: Armut,Elma,Kiwi,Muz

15-) splice()

The splice() method adds and/or removes array elements.

The splice() method overwrites the original array.

const fruits = ["Elma", "Armut", "Muz", "Portakal"];
fruits.splice(2, 0, "Limon", "Kiwi");

console.log(fruits);

OUTPUT: Elma,Armut,Limon,Kiwi,Muz,Portakal

const fruits = ["Elma", "Armut", "Muz", "Portakal", "Kiwi"]];
fruits.splice(2, 2);

console.log(fruits);

OUTPUT: Elma,Armut,Kiwi

16-) toString()

The toString() method returns a string with array values separated by commas.

The toString() method does not change the original array.

const fruits = ["Elma", "Armut", "Muz", "Portakal"];
let text = fruits.toString();

console.log(text);

OUTPUT: “Elma,Armut,Muz,Portakal” — (String)

17-) unshift()

The unshift() method adds new elements to the beginning of an array.

The unshift() method overwrites the original array.

const fruits = ["Elma", "Armut", "Muz", "Portakal"];
fruits.unshift("Limon","Ananas");

console.log(fruits);

OUTPUT: Limon,Ananas,Elma,Armut,Muz,Portakal

18-) valueOf()

The valueOf() method returns the array itself.

The valueOf() method does not change the original array.

const fruits = ["Elma", "Armut", "Muz", "Portakal"];
const myArray = fruits.valueOf();

console.log(myArray);

OUTPUT : Elma,Armut,Muz,Portakal

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