Callbacks and Higher-Order Functions

function outer() {
  const x = 10;
  return function inner(y) {
    return x + y;
  };
}

const addTen = outer();
console.log(addTen(5));

It throws an error because x is not defined in the inner function
It outputs 15
The code outputs 15. This is an example of a higher-order function (outer) that returns another function (inner). The inner function forms a closure, which means it retains access to its lexical scope - including the variable x from its parent function - even after the parent function has completed execution. When we call outer(), it returns the inner function, which we assign to addTen. When we call addTen(5), the inner function executes with y=5 and adds it to x=10, resulting in 15.
It outputs 10
It outputs undefined