Bits of .NET

📈 Hoisting = Declarations Move to Top

JavaScript hoists declarations. Understand hoisting to avoid bugs. var, let, const, function declarations — different hoisting behavior.

📝 var Hoisting

console.log(x);  // undefined (not error)
var x = 5;

// Equivalent to:
var x;
console.log(x);  // undefined
x = 5;

// Function declaration hoisting
sayHello();  // Works!

function sayHello() {
  console.log('Hello');
}

// Function expression hoisting (only declaration, not value)
sayHi();  // TypeError: sayHi is not a function
var sayHi = function() {
  console.log('Hi');
};

🎯 let and const Hoisting (Temporal Dead Zone)

console.log(x);  // ReferenceError: Cannot access 'x' before initialization
let x = 5;

// TDZ (Temporal Dead Zone)
// let and const are hoisted but not initialized
// Access before declaration = error

// const hoisting
console.log(y);  // ReferenceError
const y = 10;

// Function declaration with block scope
if (true) {
  function test() { console.log('test'); }
}
test();  // Works (function declarations hoisted to top of scope)

// Arrow functions (not hoisted)
arrow();  // ReferenceError: arrow is not defined
const arrow = () => console.log('arrow');

💡 Summary

• var: Hoisted, initialized undefined
• let/const: Hoisted, but TDZ (cannot access before declaration)
• Function declarations: Fully hoisted (can call before declaration)
• Function expressions: Only variable hoisted
• Use let/const to avoid hoisting surprises