Q73- length vs size in JavaScript?

In JavaScript, length and size are properties used to get the number of elements, but they apply to different types of objects.

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1️⃣ length

• Used for arrays, strings, and array-like objects.
• Returns the number of elements or characters.

// Array
const arr = [1, 2, 3, 4];
console.log(arr.length); // 4

// String
const str = "Hello";
console.log(str.length); // 5

Notes:

• For arrays, length reflects the highest index + 1, even if some elements are empty.

const arr2 = [];
arr2[3] = "Hi";
console.log(arr2.length); // 4

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2️⃣ size

• Used for Set and Map objects.
• Returns the number of entries in the collection.

// Set
const mySet = new Set([1, 2, 3, 3]);
console.log(mySet.size); // 3 (duplicates ignored)

// Map
const myMap = new Map();
myMap.set("a", 1);
myMap.set("b", 2);
console.log(myMap.size); // 2

Notes:

• size is read-only. You cannot set it directly.
• Unlike arrays, Set and Map only count actual elements/keys, no empty slots.

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3️⃣ Quick Comparison

Property	Works On	Counts	Example
length	Array, String	Number of elements/characters	[1,2,3].length → 3
size	Set, Map	Number of entries	new Set([1,2,2]).size → 2

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4️⃣ In short:

Use length for arrays and strings, and size for Sets and Maps — they both tell you how many elements are present, but on different object types.