Javascript Array

#Array

1. Array is object in javascript.
2. It is non-primitive type of literal.
3. It is a block of memory which is used to store multiple type of value (any type of literal) in same memory block.
4. Array 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. Values stored inside array are refered as array elements.
6. Array 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. We can access the array element with the help of array object reference , square brackets and index ( array_object_ref[index] ).
8. If we try to access the index that it greater than the array length we will get undefined.
9. Array elements should be separated by comma(,)

#Ways to create array

By using square brackets [] and literals.

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

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
- 1. It is used to insert element at last of array.
- 2. It 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
- 1. It is used to delete element from last index of array.
- 2. It returns deleted element.
- 3.
  Example:
  1let arr=[10,20,30,40,50]; 2arr.pop(); 3output: [10,20,30,40]
3. unshift(value)
- 1. It is used to insert element at first index of array.
- 2. It 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
- 1. It is used to delete element from first index of array.
- 2. It returns deleted element.
- 3.
  Example:
  1let arr=[10,20,30,40,50]; 2arr.shift(); 3output: [20,30,40,50]

5. splice() method

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

Example:

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

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]

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]

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
- 1. It is used to copy array elements.
- 2. It will not modify the original array
- 3. It 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
- 1. It used to get the index of array element.
- 2. If element is available -> it returns element's index.
- 3. If 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
- 1. It is used to check element is available or not.
- 2. If element is available -> returns true.
- 3. If 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
- 1. It is used to reverse the array.
- 2. It 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
- 1. It will modify the original array
- 2. If callback returns -ve value -> it will sort in ascending order
- 3. If callback returns +ve value -> it will sort in decending order.
- 4. If 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)
- 1. It is a higher order function.
- 2. It is used to iterate over array elements and index.
- 3. It 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)
- 1. It is a higher order function.
- 2. It is used to iterate over array.
- 3. It will not modify original array.
- 4. It returns a new array.
- 5. The 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)
- 1. It is a higher order function.
- 2. It is used to iterate over array.
- 3. It will not modify original array.
- 4. It returns a new array.
- 5. Here, 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)
- 1. It is a higher order function.
- 2. It is used to iterate and conclude result to a single value.
- 3. It will not modify original array.
- 4. It returns a single value.
- 5. Here , 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)
- 1. It is used to check given literal is array or not.
- 2. If it is array -> it will return true.
- 3. if 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)
- 1. It is used to convert iterable literals (like object or string) to array.
- 2. If literal is iterable -> it returns new array of elements.
- 3. If 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"]

#Array

#Ways to create array

By using square brackets [] and literals.

By using new keyword and Array() constructor.

#Array methods

1. push(value) method

Example:

2. pop() method

Example:

3. unshift(value)

Example:

4. shift() method

Example:

5. splice() method

Example:

Example : Delete three elements from index 1.

Example : Update value at index 3 to 500.

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

6. slice() method

Syntax :

Example : Copy array from index 0 to 2.

7. indexOf() methods

Syntax :

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

8. includes() method

Syntax :

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

9. reverse() method

Example:

10. sort(callback) method

Example : Sort array in ascending order.

Example : Sort array in descending order.

11. foreach(callback)

Syntax :

Example : Print Even numbers from given array.

12. map(callback)

Syntax :

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

13. filter(callback)

Syntax :

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

14. reduce(callback,initial_value)

Syntax :

Example : Find the sum of all elements of array.

15. Array.isArray(literal)

Example: Check given literal is array or not.

16. Array.from(literal)

Example : Convert string to Array.