What is an Array?
An Array is a special object in JavaScript used to store multiple values in a single variable.
Imagine you want to store the names of 5 students.
❌ Without Array:
let student1 = "Ram";
let student2 = "Priya";
let student3 = "Kumar";
let student4 = "John";
let student5 = "Sara";
✅ With Array:
let students = ["Ram", "Priya", "Kumar", "John", "Sara"];
Instead of creating multiple variables, we store all values inside one array.
1. Creating Arrays (2 Methods)
Method 1: Array Literal (Most Common)
This is the easiest and most commonly used method.
let fruits = ["Apple", "Mango", "Orange"];
How it works:
Index Value
0 Apple
1 Mango
2 Orange
Method 2: Array Constructor
Arrays can also be created using the Array() constructor.
let fruits = new Array("Apple", "Mango", "Orange");
Output:
["Apple", "Mango", "Orange"]
Note:
Most developers prefer the Array Literal method because it is shorter and easier to read.
Preferred:
let fruits = ["Apple", "Mango", "Orange"];
Less Common:
let fruits = new Array("Apple", "Mango", "Orange");
2. Understanding Index
Every element in an array has a position called an index.
⚠️ Array indexing starts from 0, not 1.
let fruits = ["Apple", "Mango", "Orange"];
Index Value
0 Apple
1 Mango
2 Orange
3. Accessing Array Elements
Use square brackets [] with the index number.
Example:
let fruits = ["Apple", "Mango", "Orange"];
console.log(fruits[0]); // Apple
console.log(fruits[1]); // Mango
console.log(fruits[2]); // Orange
Accessing an Invalid Index:
console.log(fruits[5]);
Output:
undefined
Because index 5 does not exist.
4. Array Length Property
The length property returns the total number of elements in an array.
Example:
let fruits = ["Apple", "Mango", "Orange"];
console.log(fruits.length);
Output:
3
Because there are 3 elements.
Another Example:
let numbers = [10, 20, 30, 40, 50];
console.log(numbers.length);
Output:
5
5. Getting the Last Element Using Length
A common interview question.
let fruits = ["Apple", "Mango", "Orange"];
console.log(fruits[fruits.length - 1]);
Output:
Orange
Explanation:
fruits.length returns 3
Last Index = 3 - 1 = 2
fruits[2] returns Orange
6. Array Elements Can Be Any Data Type
Unlike Java, JavaScript arrays can store different types of values in the same array.
Example:
let data = [
"Saravanan",
26,
true,
null
];
console.log(data);
Output:
["Saravanan", 26, true, null]
Arrays Can Store Objects
let person = [
{
name: "Saravanan",
age: 26
}
];
console.log(person);
Arrays Can Store Other Arrays
let nestedArray = [
[10, 20],
[30, 40]
];
console.log(nestedArray);
Output:
[[10,20],[30,40]]
7. Using Loops with Arrays
Arrays are commonly used with loops because they allow us to process multiple values efficiently.
Using a Traditional for Loop
let fruits = ["Apple", "Mango", "Orange"];
for (let i = 0; i < fruits.length; i++) {
console.log(fruits[i]);
}
Output:
Apple
Mango
Orange
How it Works:
1st Iteration:
i = 0
fruits[0] → Apple
2nd Iteration:
i = 1
fruits[1] → Mango
3rd Iteration:
i = 2
fruits[2] → Orange
Loop stops when:
i < fruits.length becomes false.
References:
https://www.w3schools.com/js/js_arrays.asp
https://www.geeksforgeeks.org/javascript/javascript-arrays/
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