JavaScript: Arrow Functions and Looping Methods

1. Arrow Functions

Arrow functions are a concise way to write functions in JavaScript. They do not bind their own this, arguments, or super, making them suitable for callbacks and short functions.

🔹 Syntax and Examples

// Traditional function
function square(num) {
    return num * num;
}

// Arrow function (explicit return)
const square = (num) => {
    return num * num;
}

// Arrow function (implicit return)
const square = num => num * num;

console.log(square(5)); // Output: 25

🔹 Key Features

• Shorter syntax
• Does not bind this (lexical this)
• Cannot be used with new
• No arguments object

2. Looping Methods

2.1. Normal for Loop

Best when you need to access or manipulate the index directly.

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

for (let i = 0; i < fruits.length; i++) {
    console.log(fruits[i]);
}

2.2. for...of Loop

Best when you want to iterate through values in an array or iterable.

for (const fruit of fruits) {
    console.log(fruit);
}

2.3. for...in Loop

Used for iterating over object keys.

const person = {
    name: "Girija Devi",
    age: 40,
    education: "8th passout"
};

for (const key in person) {
    console.log(key + ": " + person[key]);
}

2.4. forEach() Method

forEach is a method of the Array object. It executes a provided function once for each array element.

fruits.forEach(function(fruit, index) {
    console.log(index + " → " + fruit);
});

🔹 Key Facts About forEach

• forEach is a method, not a global function
• Belongs to Array.prototype
• Cannot be broken (no break or continue)
• Best for performing side-effects like logging or UI updates

3. When to Use Which Loop?

• for loop: When you need full control of index and want to modify the loop or break early.
• for...of: When you only need the values from an array or iterable.
• for...in: When you want to loop through the keys of an object (not suitable for arrays).
• forEach(): When you want to execute a function on each item in an array, especially for side-effects like logging or rendering.

4. Difference Table