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Javascript Array

By Saket Bhatnagar•July 5, 2025•Beginner to Intermediate

Table of Contents

  1. Array
  2. Ways to create array
  3. Array methods

Array

  1. 1Array is object in javascript.
  2. 2It is non-primitive type of literal.
  3. 3It is a block of memory which is used to store multiple type of value (any type of literal) in same memory block.
  4. 4Array size is dynamic (size is not fixed like JAVA) , it means we can store 'N' number of elements and JS engine will handle memory usage automatically.
  5. 5Values stored inside array are refered as array elements.
  6. 6Array elements are arranged in a sequence that is represented by integer number called as index. Array index starts from zero to array size - 1 (suppose array has 5 elements it's first index will be - 0 and last index will be 4).
  7. 7We can access the array element with the help of array object reference , square brackets and index ( array_object_ref[index] ).
  8. 8If we try to access the index that it greater than the array length we will get undefined.
  9. 9Array elements should be separated by comma(,)

Ways to create array

  1. 1

    By using square brackets [] and literals.

    1let arr = [];
    2// empty array
    3
    4let arr = [10,20,30];
    5// array with literals
  2. 2

    By using new keyword and Array() constructor.

    1let arr = new Array();
    2//empty array
    3
    4let arr = new Array(10,20,30)
    5//array with literals -> [10,20,30]
    NOTE : Here , 'arr' is a variable which holds the reference of array object. To access array element at index -> 1 Syntax : array_object_ref[index]Example : console.log(arr[1]); // 20

Array methods

  1. push(value) method

    • 1It is used to insert element at last of array.
    • 2It returns the length of array.
    • 3

      Example:

      1let arr=[10,20,30,40,50];
      2arr.push(100);
      3output: [10,20,30,40,50,100]
  2. pop() method

    • 1It is used to delete element from last index of array.
    • 2It returns deleted element.
    • 3

      Example:

      1let arr=[10,20,30,40,50];
      2arr.pop();
      3output: [10,20,30,40]
  3. unshift(value)

    • 1It is used to insert element at first index of array.
    • 2It returns array length
    • 3

      Example:

      1let arr=[10,20,30,40,50];
      2arr.unshift(200);
      3output: [200,10,20,30,40,50]
  4. shift() method

    • 1It is used to delete element from first index of array.
    • 2It returns deleted element.
    • 3

      Example:

      1let arr=[10,20,30,40,50];
      2arr.shift();
      3output: [20,30,40,50]
  5. splice() method

    • 1It is used to perform insertion , deletion and updation in array.
    • 2It will modify the original array.
    • 3It returns array of deleted elements.
    • 4

      Example:

      1arr_ref.splice(a,b,c)
      2a - starting index
      3b - number of elements to be deleted
      4c - elements to be inserted
    • 5

      Example : Delete three elements from index 1.

      1let arr=[10,20,30,40,50];
      2arr.splice(1,3); // deleted: [20,30,40]
      3console.log(arr);
      4
      5Output : [10,50]
    • 6

      Example : Update value at index 3 to 500.

      1let arr=[10,20,30,40,50];
      2arr.splice(3,1,500);
      3console.log(arr);
      4
      5Output : [10,20,30,500,50]
    • 7

      Example : Insert 100,200,and 300 from index 2.

      1let arr=[10,20,30,40,50];
      2arr.splice(2,0,100,200,300);
      3console.log(arr);
      4
      5Output : [10,20,100,200,300,30,40,50]
  6. slice() method

    • 1It is used to copy array elements.
    • 2It will not modify the original array
    • 3It returns array of copied elements.
    • 4

      Syntax :

      1arr.slice(a,b);
      2a - starting index
      3b - last index
      4
      5Here, last index is excluded -> last index -1
    • 5

      Example : Copy array from index 0 to 2.

      1let arr=[10,20,30,40,50];
      2let copy_elements = arr.slice(0,3);
      3console.log(copy_elements);
      4
      5Output: [10,20,30]
  7. indexOf() methods

    • 1It used to get the index of array element.
    • 2If element is available -> it returns element's index.
    • 3If element is not available -> it returns -1.
    • 4

      Syntax :

      1arr.indexOf(a,b)
      2a - value to be searched
      3b - search starting index
      4
      5If we does not pass last argument , it will 0 by default.
      6
    • 5

      Example : Check given array has element 30 or not and search from index 0 and 3 , if present print index.

      1let arr=[10,20,30,40,50];
      2console.log(arr.indexOf(30)); // 2
      3console.log(arr.indexOf(30,3)); // -1
      4
  8. includes() method

    • 1It is used to check element is available or not.
    • 2If element is available -> returns true.
    • 3If element is not available -> returns false.
    • 4

      Syntax :

      1arr_ref.includes(a,b);
      2a - value to be searched
      3b - search starting index
      4
      5If we does not pass last argument , it will 0 by default.
    • 5

      Example : Check given array has element 30 or not and search from index 0 and 3 , if present print true.

      1let arr=[10,20,30,40,50];
      2console.log(arr.includes(30)); // true
      3console.log(arr.includes(30,3)); // false
      4
  9. reverse() method

    • 1It is used to reverse the array.
    • 2It will modify the original array.
    • 3

      Example:

      1let arr=[10,20,30,40,50];
      2console.log(arr.reverse());
      3
      4Output: [50,40,30,20,10]
  10. sort(callback) method

    • 1It will modify the original array
    • 2If callback returns -ve value -> it will sort in ascending order
    • 3If callback returns +ve value -> it will sort in decending order.
    • 4If callback returns 0 value -> it will not sort.
    • 5

      Example : Sort array in ascending order.

      1let arr = [100, 2000, 380, 940, 50, 0, 2];
      2console.log(arr.sort((a, b) => a - b));
      3
      4Output: [ 0, 2, 50, 100, 380, 940, 2000 ]
    • 6

      Example : Sort array in descending order.

      1let arr = [100, 2000, 380, 940, 50, 0, 2];
      2console.log(arr.sort((a, b) => b - a));
      3
      4Output: [ 2000, 940, 380, 100, 50, 2, 0 ]
  11. foreach(callback)

    • 1It is a higher order function.
    • 2It is used to iterate over array elements and index.
    • 3It doesnot return anything , so js engine implicitly returns undefined.
    • 4

      Syntax :

      1arr_ref.foreach((value,index,array)=>{
      2 // statements
      3})
    • 5

      Example : Print Even numbers from given array.

      1const arr = [1, 2, 3, 4, 5];
      2arr.forEach((val)=> {
      3 if(val % 2 === 0)
      4 {
      5 console.log(val+" "+"is even number;");
      6 }
      7});
  12. map(callback)

    • 1It is a higher order function.
    • 2It is used to iterate over array.
    • 3It will not modify original array.
    • 4It returns a new array.
    • 5The value returned by callback function will be inserted in new array , if it doesnot return anything 'undefined' will be stored.
    • 6

      Syntax :

      1arr_ref.map((value,index,array)=>{
      2 // statements
      3})
    • 7

      Example: Create new array where each element of given array is multiple of 8.

      1let arr=[10,20,30,40,50];
      2let new_arr = arr.map(value => value * 8 );
      3console.log(new_arr);
      4
      5Output: [80,160,240,320,400]
  13. filter(callback)

    • 1It is a higher order function.
    • 2It is used to iterate over array.
    • 3It will not modify original array.
    • 4It returns a new array.
    • 5Here, element will be inserted in new array only when callback function returns true.
    • 6

      Syntax :

      1arr_ref.filter((value,index,array)=>{
      2 // statements
      3})
    • 7

      Example: Create new array where elements are greater than 40.

      1let arr=[10,20,30,40,50,60,70];
      2let new_arr = arr.filter(value => {
      3 if(value > 30)
      4 return true;
      5});
      6console.log(new_arr);
      7
      8Output: [40,50,60,70]
  14. reduce(callback,initial_value)

    • 1It is a higher order function.
    • 2It is used to iterate and conclude result to a single value.
    • 3It will not modify original array.
    • 4It returns a single value.
    • 5Here , single value is returned after complete iteration of array. Value is stored in a variable which is used to result , we refer it as accumulator.
    • 6

      Syntax :

      1arr_ref.reduce((accumulator,value,index,array)=>{
      2 // statements
      3},initial_value_of_accumulator)

      If we does not pass initial value of accumulator first element of array will be stored automatically.

    • 7

      Example : Find the sum of all elements of array.

      1let arr=[10,20,30,40,50,60,70];
      2let result = arr.reduce((acc,value) => {
      3 acc = acc + value;
      4 return acc;
      5},0);
      6console.log("Sum of all elements : ",result);
      7
      8Output: Sum of all elements : 280
      9
  15. Array.isArray(literal)

    • 1It is used to check given literal is array or not.
    • 2If it is array -> it will return true.
    • 3if it is not array -> it will return false.
    • 5

      Example: Check given literal is array or not.

      1console.log(Array.isArray({})); //false
      2console.log(Array.isArray(10)); //false
      3console.log(Array.isArray([10,20,30])); //true
  16. Array.from(literal)

    • 1It is used to convert iterable literals (like object or string) to array.
    • 2If literal is iterable -> it returns new array of elements.
    • 3If literal is not iterable -> it returns empty array.
    • 4

      Example : Convert string to Array.

      1const str = "hello";
      2const arr = Array.from(str);
      3console.log(arr);
      4
      5Output: ["h", "e", "l", "l", "o"]

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Last updated: August 5, 2025

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