Portée de bloc, de fonction et de module, et TDZ

Introduction

Démonstration de la portée de bloc

// Block scope: let/const exist only inside the braces
let lives = 3;

if (true) {
  const bonus = 5;
  let level = 1;
  console.log("Inside block:", bonus, level);
}

console.log("Lives:", lives);
// Uncommenting next line would fail (not in scope):
// console.log(bonus, level);

Portée de fonction avec var

// Function scope: var is visible across the whole function
function demo() {
  if (true) {
    var x = 10; // function-scoped
  }
  console.log("x is visible here:", x); // 10
}
demo();

Bases de la portée de module

// Module scope: top-level variables are local to the module file
const appName = "CoddyKit";
console.log("App name:", appName);

// In a real project, this would be its own file/module.
// Other files must import to access appName.

Zone morte temporelle

// TDZ: using let/const before declaration throws ReferenceError
try {
  // Uncommenting would trigger TDZ:
  // console.log(mode); // ReferenceError
  let mode = "dark";
  console.log("Mode after declare:", mode);
} catch (e) {
  console.log("Caught:", e.message);
}

Pièges liés à la portée

Question sur TDZ

Récapitulatif