"𝗡𝘂𝗹𝗹 𝗮𝗻𝗱 𝗨𝗻𝗱𝗲𝗳𝗶𝗻𝗲𝗱 𝗶𝗻 𝗝𝗮𝘃𝗮𝗦𝗰𝗿𝗶𝗽𝘁: 𝗧𝗵𝗲 𝗙𝗶𝗻𝗲 𝗟𝗶𝗻𝗲 𝗕𝗲𝘁𝘄𝗲𝗲𝗻 𝗧𝗵𝗲𝗺"

📗 𝗪𝗵𝗮𝘁 𝗶𝘀 𝗡𝘂𝗹𝗹?
We have heard the word "null" many times in English. Its literal meaning is having no value. The same meaning is analogous to the meaning of null in programming.

Null in JavaScript is a specific value that represents the intentional absence of any object value. When we assign null as a value to a variable, it means that the variable is intentionally empty or blank. This is different from undefined, which represents the absence of any value, including both object and primitive values.

Although typeof null returns "object", null is actually a primitive value type in JavaScript, like undefined, boolean, number, string, and symbol.

var x = null;
Here we have assigned the value null to variable x.

✅ 𝗪𝗵𝗮𝘁 𝗶𝘀 𝗨𝗻𝗱𝗲𝗳𝗶𝗻𝗲𝗱?
As the name suggests, undefined means "not defined". So if we declare a variable but do not assign a value to it, the variable becomes undefined.

Unlike null, the value of an undefined variable is set by JavaScript as undefined. The variable gets created at run-time. When we do not pass an argument for a function parameter, the default value is taken as undefined. Additionally, when a function doesn't return a value, it returns undefined.

var x;
console.log(typeof(x)); // undefined

Here we have declared variable x and then checked its type. During run-time, undefined gets assigned to the variable x.

In JavaScript, null and undefined are both used to represent the absence of a value. However, they have slightly different behaviors when used in arithmetic operations.

When null is used in arithmetic operations, it gets converted to the number 0. This is because the 𝘁𝗼𝗡𝘂𝗺𝗯𝗲𝗿() function is called on null, which converts it to 0. Therefore, any arithmetic operation performed on null will result in 0.

On the other hand, when undefined is used in arithmetic operations, it gets converted to NaN (Not a Number). This is because 𝘁𝗼𝗡𝘂𝗺𝗯𝗲𝗿() function called on undefined converts it to NaN.

var length = 19;
var breadth;
var area = length*breadth;
console.log(area); // NaN

var length2 = 19;
var breadth2 = null;
var area2 = length2 * breadth2;
console.log(area2); // 0

The variable 'breadth' is undefined, so when we try to calculate the area of the rectangle, the result is NaN. On the other hand, the variable 'breadth2' is null, so when we try to calculate the area of the rectangle, the result is 0.

Understanding the difference between null and undefined is important in writing bug-free and efficient code.

That's all for today 🙂

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