30-seconds-of-code/snippets/once.md

once

Ensures a function is called only once.

Utilizing a closure, use a flag, called, and set it to true once the function is called for the first time, preventing it from being called again. Allow the function to be supplied with an arbitrary number of arguments using the spread (...) operator.

const once = fn => {
  let called = false;
  return (...args) => {
    if (!called) {
      fn(...args);
      called = true;
    }
  };
};

const startApp = event => {
  // initializes the app
  console.log(event); // access to any arguments supplied
};
document.addEventListener('click', once(startApp)); // only runs `startApp` once upon click