“Undefined” in javascript: Amazing Cases.

📗 𝐓𝐡𝐞 𝐂𝐮𝐫𝐢𝐨𝐮𝐬 𝐂𝐚𝐬𝐞 𝐨𝐟 “𝐔𝐧𝐝𝐞𝐟𝐢𝐧𝐞𝐝” 𝐢𝐧 𝐉𝐚𝐯𝐚𝐒𝐜𝐫𝐢𝐩𝐭

👉 In JavaScript, “undefined” is a primitive data type that represents a value that is not assigned to a variable or a property. “undefined” is a property of the global object. That is, it is a variable in global scope.

JavaScript uses the undefined value in the following situations.

✅ 1) 𝐀𝐜𝐜𝐞𝐬𝐬𝐢𝐧𝐠 𝐚𝐧 𝐮𝐧𝐢𝐧𝐢𝐭𝐢𝐚𝐥𝐢𝐳𝐞𝐝 𝐯𝐚𝐫𝐢𝐚𝐛𝐥𝐞
When we declare a variable and don’t initialize it to a value, the variable will have a value of ”undefined”.
For example:

let x;
console.log(x); // Output: undefined

✅ 2) 𝐀𝐜𝐜𝐞𝐬𝐬𝐢𝐧𝐠 𝐚 𝐧𝐨𝐧-𝐞𝐱𝐢𝐬𝐭𝐢𝐧𝐠 𝐩𝐫𝐨𝐩𝐞𝐫𝐭𝐲 𝐨𝐟 𝐚𝐧 𝐨𝐛𝐣𝐞𝐜𝐭
If we access a non-existing property of an object, we’ll get undefined.
For example:

let person = {
name: "Sachin",
};
console.log(person.age); // undefined

In this example, the person object has one property “name”. Accessing the “age” property that doesn’t exist on the “person” object returns undefined.

✅ 3) 𝐅𝐮𝐧𝐜𝐭𝐢𝐨𝐧 𝐩𝐚𝐫𝐚𝐦𝐞𝐭𝐞𝐫𝐬
when we call the function and don’t pass all the arguments, the parameters inside the function become undefined.
For example:

const calculation = (a, b ) => {
  return b === 7 ? ${ a } : ${ a} ${ b };
}
calculation(3); // 3 undefined

✅ 4) 𝐅𝐮𝐧𝐜𝐭𝐢𝐨𝐧𝐬 𝐫𝐞𝐭𝐮𝐫𝐧 𝐚 𝐯𝐚𝐥𝐮𝐞
A function that doesn’t have a return statement implicitly returns undefined.
For example:

function myFunc() {
// Do something but don't return a value
}
console.log(myFunc()); // Output: undefined

✅ 5) 𝐀𝐜𝐜𝐞𝐬𝐬𝐢𝐧𝐠 𝐨𝐮𝐭-𝐨𝐟-𝐛𝐨𝐮𝐧𝐝𝐬 𝐚𝐫𝐫𝐚𝐲 𝐞𝐥𝐞𝐦𝐞𝐧𝐭𝐬
When we access an array element that is out-of-bounds, we’ll get the undefined value.
For example:

const colors = ['red', 'green', 'blue'];
console.log(colors[3]); // undefined`

👉 𝐒𝐮𝐦𝐦𝐚𝐫𝐲
✅ The undefined is a primitive type that has a single value undefined.
✅ Accessing an uninitialized variable returns undefined.
✅ Accessing a non-existing property of an object returns undefined.
✅ Accessing an out-of-bounds array element returns undefined.
✅ A function without a return statement or with a return statement but without an expression returns undefined.

That’s all for today 🙂

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