flowchart TD
    subgraph Compilation["Compilation Phase (Before Execution)"]
        A1["var x → memory: undefined"]
        A2["function greet() → entire function in memory"]
        A3["let y → memory: TDZ (uninitialized)"]
    end

    subgraph Execution["Execution Phase (Line by Line)"]
        B1["console.log(x) // undefined"]
        B2["x = 5 // assignment runs"]
        B3["console.log(y) // ❌ ReferenceError (TDZ)"]
        B4["let y = 10 // TDZ ends"]
    end

    Compilation --> Execution

// 1. var — hoisted, initialized as undefined
console.log(a); // undefined
var a = 5;

// 2. let — hoisted, but in TDZ (uninitialized)
console.log(b); // ❌ ReferenceError
let b = 10;

// 3. const — same as let (hoisted, TDZ)
console.log(c); // ❌ ReferenceError
const c = 15;

// 4. Function declarations — fully hoisted
greet(); // "Hello!" — entire function is hoisted
function greet() {
  console.log("Hello!");
}

// 5. Function expressions — only variable hoisted
// sayHi(); // ❌ TypeError: sayHi is not a function
var sayHi = function() {
  console.log("Hi!");
};