JavaScript Indexed Collections

Javascript Indexed Collections are collections that have numeric indices i.e. the collections of data that are ordered by an index value. In JavaScript, an array is an indexed collection. An array is an ordered set of values that has a numeric index.

For example, an array called ‘student’ contains the name of the students and the index values are the Roll Numbers of the students. JavaScript does not have an explicit array data type. However, we can use the predefined Array object in JavaScript and its methods to work with arrays.

Creating an Array: There are many ways to create and initialize an array that is listed below:

Creating arrays without defining the array length. In this case, the length is equal to the number of arguments.

Syntax:

let arr = new Array( element0, element1, ... );   
let arr = Array( element0, element1, ... );       
let arr = [ element0, element1, ... ];

Creating an array with the given size

Syntax:

let arr = new Array(6); 

let arr = Array(6);

let arr = [];
arr.length = 6;

Create a variable-length array and add many elements as you need.

// First method: Initialize an empty
// array then add elements
let students = [];
students [0] = 'Sujata Singh';
students [1] = 'Mahesh Kumar';
students [2] = 'Leela Nair';
 
// Second method: Add elements to
// an array when you create it
let fruits = ['apple', ‘mango', 'Banana'];

The methods that can be applied over arrays are:

Method 1: Accessing the Array Elements

Use indices to access array elements. Indices of Arrays are zero-based which means the index of the elements begins with zero.

javascript

let fruits = ['Apple', 'Mango', 'Banana'];
console.log(fruits [0]);
console.log(fruits[1]);

Output

Apple
Mango

Method 2: Obtaining array length

To obtain the length of an array use array_name.length property.

javascript

let fruits = ['Apple', 'Mango', 'Banana'];
console.log(fruits.length)

Output

Method 3: Iterating over arrays

There are many ways to iterate the array elements.

JavaScript for loop: for loop provides a concise way of writing the loop structure. Unlike a while loop, a for statement consumes the initialization, condition, and increment/decrement in one line thereby providing a shorter, easy-to-debug structure of looping.

javascript

const fruits = ['Apple', 'Mango', 'Banana'];

for (let i = 0; i < fruits.length; i++) {

    console.log(fruits[i]);
}

Output

Apple
Mango
Banana

JavaScript forEach() Loop: The forEach() function provides once for each element of the array. The provided function may perform any kind of operation on the elements of the given array.

javascript

const fruits = ['Apple', 'Mango', 'Banana'];

fruits.forEach(function (fruit) {

    console.log(fruit);
});

Output

Apple
Mango
Banana

JavaScript forEach Loop with Arrow Functions:

javascript

const fruits = ['Apple', 'Mango', 'Banana'];
fruits.forEach(fruit => console.log(fruit));

Output

Apple
Mango
Banana

Method 4: Array Methods

There are various array methods available to us for working on arrays. These are:

JavaScript push() Method: This method adds one or more elements to the end of an array and returns the resulting length of the array.

javascript

let numbers = new Array('1', '2');

numbers.push('3');
console.log(numbers);

Output

[ '1', '2', '3' ]

JavaScript pop() Method: This method removes the last element from an array and returns that element.

javascript

let numbers = new Array('1', '2', '3');
let last = numbers.pop();
console.log(last);

Output

JavaScript concat() Method: This method joins two arrays and returns a new array.

javascript

let myArray = new Array('1', '2', '3');

myArray = myArray.concat('a', 'b', 'c');
console.log(myArray);

Output

[ '1', '2', '3', 'a', 'b', 'c' ]

JavaScript join() Method: This method creates a string by joining all the elements of an array.

javascript

let students = new Array('john', 'jane', 'joe');

let list = students.join(' - ');
console.log(list);

Output

john - jane - joe

JavaScript sort() Method: This method sorts the elements of an array.

javascript

let myArray = new Array('West', 'East', 'South');
myArray.sort();
console.log(myArray);

Output

[ 'East', 'South', 'West' ]

JavaScript indexOf() Method: This method searches the array for an Element and returns the index of the first occurrence of the element.

javascript

let myArr = ['a', 'b', 'a', 'b', 'a'];

console.log(myArr.indexOf('b'));

Output

JavaScript shift() Method: This method removes the first element from an array and returns that element.

javascript

let myArr = new Array('a', 'b', 'c');
let first = myArr.shift();
console.log(first);

Output

JavaScript reverse() Method: This method reverses the first array element become the last and the last becomes the first. It transposes all the elements in an array in this manner and returns a reference to the array.

javascript

let myArr = new Array('a', 'b', 'c');
myArr.reverse();
console.log(myArr);

Output

[ 'c', 'b', 'a' ]

JavaScript map() Method: This method returns a new array of the returned value from executing a function on every array item.

javascript

let myArr1 = ['a', 'b', 'c'];

let a2 = myArr1.map(function (item) {

    return item.toUpperCase();
});
console.log(a2);

Output

[ 'A', 'B', 'C' ]

JavaScript filter() Method: This method returns a new array containing the items for which the function returned true.

javascript

let myArr1 = ['a', 10, 'b', 20, 'c', 30];
 
let a2 = myArr1.filter(function (item) {

    return typeof item === 'number';
});
 
console.log(a2);

Output

[ 10, 20, 30 ]

Article Tags :

JavaScript

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