What are rest parameters and how do they differ from the arguments object?

Rest parameters (...args) collect remaining function arguments into a real Array.

// Rest parameters — modern
function sum(first, ...rest) {
  console.log(first);   // 1
  console.log(rest);    // [2, 3, 4] — real Array!
  return rest.reduce((a, b) => a + b, first);
}
sum(1, 2, 3, 4); // 10
rest.map(x => x * 2); // ✅ has Array methods

// arguments — legacy
function old() {
  console.log(arguments);        // { 0:1, 1:2, ... } — array-LIKE
  console.log(arguments.map);    // undefined — NOT a real Array
  const arr = Array.from(arguments); // convert needed
}

// Arrow functions have NO arguments object
const arrow = () => {
  console.log(arguments); // ReferenceError!
  // Use rest: (...args) => { console.log(args) }
};

Key differences:

• Rest is a real Array → has all array methods
• arguments is array-like → no map/filter/etc
• Arrow functions don't have arguments
• Rest collects only the remaining args after named params