• An array is an ordered list of values that you refer to with a name and an index.

const array1 = new Array(1,2,3,4,5,6);
const array2 = Array(1,2,3,4,5,6);
const array3 = [1,2,3,4,5,6]; //Array literal 
console.log("Array1:", array1);
console.log("Array2:", array2);
console.log("Array3:", array3);

Output:

Array1: [ 1, 2, 3, 4, 5, 6 ]
Array2: [ 1, 2, 3, 4, 5, 6 ]
Array3: [ 1, 2, 3, 4, 5, 6 ]

• If you wish to initialize an array with a single element, and the element happens to be a Number, you must use the bracket syntax.
• When a single Number value is passed to the Array() constructor or function, it is interpreted as the length of the array, not as a single element.

const length = 10;
const array4 = Array(length);
const array5 = new Array(length);
const array6 = [];
console.log("Array 4:",array4); 
console.log("Array 5:",array5); 
console.log("Array 6:",array6); 

Output:

Array 4: [ <10 empty items> ]
Array 5: [ <10 empty items> ]
Array 6: []

• In the above code, length must be a Number.
• Otherwise, an array with a single element (the provided value) will be created.
• Calling Array(N) results in a RangeError, if N is a non-whole number whose fractional portion is non-zero.

const  employees = {
    names:['Mahedi', 'Hassan', 'Shawon']
};;
employees.id =[1, 2, 3];
console.log('Employee Information: ',employees);

Output:

Employee Information:  { names: [ 'Mahedi', 'Hassan', 'Shawon' ], id: [ 1, 2, 3 ] }

const array7 = Array.of(5.1);
console.log("Array 7:",array7); 

Output:

Array 7: [ 5.1 ]

console.log(array1[0]);
console.log(array1[3]);
console.log(array1['length']);

Output:

1
4
6

const student = [];
student[0] = 'Mahedi';
student[1] = 'Hassan';
student[2] = 'Shawon';
student[3.1] = 'Chief'
console.log(student)
const teacher = new Array('teacher1', 'teacher2', 'teacher3');
console.log(teacher);
console.log("Array length of student is:", student.length);

Output:

[ 'Mahedi', 'Hassan', 'Shawon', '3.1': 'Chief' ]
[ 'teacher1', 'teacher2', 'teacher3' ]
Array length of student is: 3

• Here length of the student array is 3. Because,when we use non-integer indices with arrays, they are treated as properties of the array object, not as actual array elements.

const staff = ['Mahedi', 'Hassan','Shawon'];
console.log('Staff array length:',staff.length);
console.log('Staffs :',staff);
staff.length = 2;
console.log('Staffs :',staff);

Output:

Staff array length: 3
Staffs : [ 'Mahedi', 'Hassan', 'Shawon' ]
Staffs : [ 'Mahedi', 'Hassan' ]

let nums = [1,2,3,4,5,6,7,8,9,10];
for(let i =0; i<nums.length; i++)
{
    console.log(nums[i]);
}
//Method 2
nums = [1,,3,,5];
nums.forEach(num=> {
    console.log(num);
});

Output:

2
3
4
5
6
7
8
9
10
1
3
5

• Please bear in mind that when an array is defined with omitted elements, those elements won't appear during iteration using forEach. However, if undefined is manually assigned to an element, it will be listed during iteration.

//concat()
let teacher = new Array("teacher1", "teacher2", "teacher3");
const staff = ["Mahedi", "Hassan"];
//concat()
const totalEmployees = teacher.concat(staff);
console.log("Total employees after concat(): ",totalEmployees);
//join()
const list = totalEmployees.join("*");
console.log("Total employees after join(): ",list);
//push()
totalEmployees.push("Potato");
console.log("Total employees after push(): ",totalEmployees);
//pop()
totalEmployees.pop();
console.log("Total employees after pop(): ",totalEmployees);
//shift()
totalEmployees.shift();
console.log("Total employees after shift(): ",totalEmployees);
//unshift()
totalEmployees.unshift('teacher1');
console.log("Total employees after unshift(): ",totalEmployees);
//slice()
const sliced = totalEmployees.slice(1, 4);
console.log("Sliced: ",sliced );
//at()
console.log(sliced.at(-2));
//reverse()
console.log('Sliced reversed',sliced.reverse());
//sort()
const numbers = [10,9,8,7,6,5,4,3,2,1];
console.log("Ascending order:",numbers.sort((a,b)=>a-b));
console.log("Descending order:",numbers.sort((a,b)=>b-a));
//map()
const mappedNumbers = numbers.map((number)=>{
  return number + 10;
})
console.log("Mapped Numbers Array:",mappedNumbers);
//filter()
const evenNumbers = numbers.filter((number)=>{
  return number%2 === 0;
})
console.log("Even Numbers Array:",evenNumbers);

Output:

Total employees after concat():  [ 'teacher1', 'teacher2', 'teacher3', 'Mahedi', 'Hassan' ]
Total employees after join():  teacher1*teacher2*teacher3*Mahedi*Hassan
Total employees after push():  [ 'teacher1', 'teacher2', 'teacher3', 'Mahedi', 'Hassan', 'Potato' ]
Total employees after pop():  [ 'teacher1', 'teacher2', 'teacher3', 'Mahedi', 'Hassan' ]
Total employees after shift():  [ 'teacher2', 'teacher3', 'Mahedi', 'Hassan' ]
Total employees after unshift():  [ 'teacher1', 'teacher2', 'teacher3', 'Mahedi', 'Hassan' ]
Sliced:  [ 'teacher2', 'teacher3', 'Mahedi' ]
teacher3
Sliced reversed [ 'Mahedi', 'teacher3', 'teacher2' ]
Ascending order: [
  1, 2, 3, 4,  5,
  6, 7, 8, 9, 10
]
Descending order: [
  10, 9, 8, 7, 6,
   5, 4, 3, 2, 1
]
Mapped Numbers Array: [
  20, 19, 18, 17, 16,
  15, 14, 13, 12, 11
]
Even Numbers Array: [ 10, 8, 6, 4, 2 ]

• concat():

  • Takes arrays and combines them into a new array.
  • Original arrays remain unchanged.
  • Used here to concatenate the teacher and staff arrays into a new array named totalEmployees.

• join():

  • Combines array elements into a single string.
  • Elements are separated by the specified delimiter.
  • Used here to join the elements of the totalEmployees array with '*' as the delimiter.

• push():

  • Adds one or more elements to the end of an array.
  • Modifies the original array.
  • Used here to add the string "Potato" to the end of the totalEmployees array.

• pop():

  • Removes the last element from an array.
  • Modifies the original array.
  • Used here to remove the last element from the totalEmployees array.

• shift():

  • Removes the first element from an array.
  • Modifies the original array.
  • Used here to remove the first element from the totalEmployees array.

• unshift():

  • Adds one or more elements to the beginning of an array.
  • Modifies the original array.
  • Used here to add the string 'teacher1' to the beginning of the totalEmployees array.

• slice():

  • Extracts a portion of an array into a new array.
  • Original array remains unchanged.
  • Used here to create a new array sliced containing elements from index 1 to index 3 (exclusive) of totalEmployees.

• at():

  • Returns the element at a specified index in an array.
  • Negative index values are counted from the end of the array.
  • Used here to log the element at the second-to-last position of the sliced array.

• reverse():

  • Reverses the elements of an array.
  • Modifies the original array.
  • Used here to reverse the elements of the sliced array.

• sort():

  • Arranges the elements of an array in ascending or descending order.
  • Modifies the original array.
  • Used here to sort the numbers array in both ascending and descending orders.

• map():

  • Creates a new array by applying a function to each element in an existing array.
  • Used here to create a new array mappedNumbers by adding 10 to each element of the numbers array.

• filter():

  • Creates a new array with elements that satisfy a given condition.
  • Used here to create a new array evenNumbers containing only the even numbers from the numbers array.

• MDN Web Docs - Indexed collections: Used as a reference for these notes.