exercise.js

/*
    By now, you would have already seen "undefined", either in an error message or being output from your program.
    But what does it mean? undefined represents the absence of a value.
    
    In some cases, undefined will be used by a programmer intentionally, and they will write code to handle it.
    But usually, when you see undefined - it means something has gone wrong!

    Below are 4 typical examples of when you would see undefined.
    For each example, can you explain why we are seeing undefined?
*/

// Example 1
let a;
console.log(a);

//because "a" did not assign to any value
// let a = 2;
// console.log(a)


// Example 2
function sayHello() {
    let message = "Hello";
}

//I think because 'message' is declared but its value is never read.

// function sayHello() {
//     let message = "Hello";
//     return message
// }

let hello = sayHello();
console.log(hello);


// Example 3
function sayHelloToUser(user) {
    console.log(`Hello ${user}`);
}


sayHelloToUser();

// any returned value
// function sayHelloToUser(user) {
//     let userName = user
//     console.log(`Hello ${userName}`);
//     return `Hello ${userName}`
// }



// Example 4
let arr = [1, 2, 3];
console.log(arr[3]);

//non-existing array element