Day 1 · Welcome & Variables

Hands-on

Task 1 Hello World
  • Print "Hello, World!" with console.log.
  • Declare a const for your name and log it.
  • Log one line that uses + to build: name + " is learning JS".

console.log("Hello, World!");

const name = "Kalyan"; // replace with your name
console.log(name);

console.log(name + " is learning JS");

Check the browser console (F12 → Console) when you run day-1/js/hands-on.js via this page.

Task 2 let vs const
  • Create let age = 25. Log it.
  • Reassign age = 26 Log it again. Confirm the new value.
  • create const PI = 3.14 Try to reassign PI = 3.15. Note the error.
  • Create let cityName (no value yet). Log it. Then assign "Jaipur" . Log again.

let age = 25;
console.log(age); // 25

age = 26;
console.log(age); // 26 (updated)

// const cannot be reassigned
const PI = 3.14;
console.log(PI);


// declare without value
let cityName;
console.log(cityName); // undefined

cityName = "Jaipur";
console.log(cityName); // Jaipur

Reference behaviour is implemented in ../js/hands-on.js (loaded below).

Task 3 Block Scope
  • Create a block { let x = 10; console.log(x); } . Run it
  • Now try to log x AFTER the block. Note the error.
  • Inside an if (true) { ... } block, declare let inside = "hi" and log it.
  • Try logging inside outside the if. Note the error.

                     
{
  let x = 10;
  console.log(x); // 10
}



if (true) {
  let inside = "hi";
  console.log(inside); // hi
}

Reference behaviour is implemented in ../js/hands-on.js (loaded below).

Bonus var Pitfall
  • Inside a for (var i = 0; i < 3; i++) { } loop, log i AFTER the loop ends.
  • Note that i is still accessible — it leaked out!
  • Now do the same with let i . Try logging i after — note the error
  • In a comment, write WHY this matters.

for (var i = 0; i < 3; i++) {}

console.log(i);