Map vs Object — When to Use Each

// Map accepts ANY key type — objects, functions, numbers
const m = new Map();
const keyObj = {};
m.set(keyObj, 'value');
m.set(42, 'the answer');

// Maintains insertion order (Object does too now, mostly)
// Has a reliable .size property
console.log(m.size);  // 2

// Iteration is simpler
for (const [key, val] of m) console.log(key, val);

// Object is better for JSON serialization
JSON.stringify(m);  // '{}' — Map doesn't serialize!