A demonstration of how to use JavaScript closures to create a logged function. The inner function creates a closure containing a function that is passed into the outer function. Each time the inner function is called, it logs that name, arguments, and UTC time that the function in the closure was called.

closureLogger.js

function createLoggedFunction(fn) {
  function loggedFunction(...args) {
    const nowUtc = new Date().getTime();
    
    console.log('----Start----');
    console.log(`Function ${fn.name} was called with ${args} at ${nowUtc}`);
    console.log('-----End-----');
    
    return fn(...args);
  };

  return loggedFunction;
};

function add(a, b) {
  return a + b;
};

const logAdd = createLoggedFunction(add);
const sum = logAdd(100, 300);