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Go through arrays in JavaScript (Part II)

Lets talk about array and some more array methods

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Omkar Chaskar
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Table of contents

Hey guys , welcome to Omkar's blogs . Today we talk about some more array methods. Here are some array methods -

  • lastIndexOf()
  • indexOf()
  • findIndex()
  • reverse()
  • sort()
  • fill()
  • find()
  • includes()


lastIndexOf()

The lastIndexof() method returns the index of last occurrence of a specific element in an array.

const numList = [5, 12, 11, 22, 11, 55, 11, 24];
console.log(numList.lastIndexOf(11));
// output : 6

lastIndexOf() method return last index as 6 . Also we can pass two parameters :

  • First parameter is the element to search.
  • Second Parameter is the index value from where we have to start searching for element in backward way. 
    const numList = [5, 12, 11, 22, 11, 55, 11, 24];
console.log(numList.lastIndexOf(11 , 5));
// output : 4

indexOf()

The indexof() method returns the index of first occurrence of a specific element in an array.

const numList = [5, 12, 11, 22, 11, 55, 11, 24];
console.log(numList.indexOf(11));
// output : 2

The indexOf() method return last index as 2 . Also we can pass two parameters :

  • First parameter is the element to search.
  • Second Parameter is the index value from where we have to start searching for element. By default , it is 0. 
    const numList = [5, 12, 11, 22, 11, 55, 11, 24];
console.log(numList.lastIndexOf(11 , 5));
// output : 6
    Returns -1 if the element is not found in the array.

findIndex()

The findIndex() method also returns the index of first occurrence when the conditions are satisfies in function.

// defining an array of integers
const numList = [5, 12, 11, 22, 11, 55, 11, 24];

// function that returns odd number
function isEven(element) {
  return element % 2 == 0;
}

// returns the index of the first odd number in the array
let firstEven = numList.findIndex(isEven);

console.log(firstEven);

// Output: 1

The findIndex() method return first index as 1 . Also we can pass two parameters :

  • First parameter is callback function , which execute on each element of an array.
  • Second Parameter is optional parameter . It is a object to use as this inside callback.

Returns -1 if none of the elements satisfy the function.

reverse()

The reverse() method returns the array in reverse order.

const numList = [5, 12, 11, 22, 11, 55, 11, 24];
console.log(numList.reverse());
// output : [24, 11, 55, 11, 22, 11, 12, 5]

The reverse() method create new array with reversed array elements.

sort()

The sort() method is use to sort elements of an array in ascending or descending order.

const fruits = ["Banana", "Orange", "Grapes", "Pineapple", "Apple", "Mango"];
console.log(fruits.sort());

//['Apple', 'Banana', 'Grapes', 'Mango', 'Orange', 'Pineapple']

In sort() method, we can pass a parameter as a compare function to sort in custom order.

If we want to sort a number array then, the sort() method convert number into staring and then sort then. 

const numList = [5 , 1, 55, 22, 44, 100 , 1111, 154];
console.log(numList.sort());
// Output : [1, 100, 1111, 154, 22, 44, 5, 55]

To solve this problem we can do this -

// custom sorting an array of numbers
const numList = [5 , 1, 55, 22, 44, 100 , 1111, 154];

function compare(a, b){
    return a - b;
}

// sort according to numbers
numList.sort(compare);

console.log(numList);

//Output : [1, 5, 22, 44, 55, 100, 154, 1111]

fill()

The fill() method returns an array by filling all elements with a specified value.

const fruits = ["Banana", "Orange", "Grapes", "Pineapple", "Apple"];
console.log(fruits.fill("Mango"));
// Output : ['Mango', 'Mango', 'Mango', 'Mango', 'Mango']

In fill() method , we can also pass 3 parameters -

  • First parameter is a value to fill with.
  • Second parameter is starting index.
  • Third parameter is ending index.
const fruits = ["Banana", "Orange", "Grapes", "Pineapple", "Apple"];
console.log(fruits.fill("Mango" , 1 , 3));
// Output : ['Banana', 'Mango', 'Mango', 'Pineapple', 'Apple']

Since fill() is a mutator method, it returns the array itself . Not a copy of an array with change values.

find()

The find() method also returns the index of first occurrence when the conditions are satisfies in function.

// defining an array of integers
const numList = [5, 12, 11, 22, 11, 55, 11, 24];

// function that returns odd number
function isEven(element) {
  return element % 2 == 0;
}

// returns the index of the first odd number in the array
let firstEven = numList.find(isEven);

console.log(firstEven);

// Output: 12

The find() method return first index as 12 . Also we can pass two parameters :

  • First parameter is callback function , which execute on each element of an array.
  • Second Parameter is optional parameter . It is a object to use as this inside callback.

Returns undefined if none of the elements satisfy the function.

includes()

The includes() method checks if an array contains a specified element or not.

const fruits = ["Banana", "Orange", "Grapes", "Pineapple", "Apple"];
console.log(fruits.includes("Orange" ));
// Output : true

In include() method, we can pass two parameters -

  • First paramertet is value to be search.
  • Second parameter is the position in the array at which to begin the search.
const fruits = ["Banana", "Orange", "Grapes", "Pineapple", "Apple"];
console.log(fruits.includes("Orange" , 2 ));
// Output : false

Thanks you for reading my blog. Some more array methods are in my next blog .

Please read and enjoy array methods.

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