Function once

lib/index.js:92–104

(fun)

}

function once(fun) {
  var called = false;
  return function (...args) {
    /* istanbul ignore if */
    if (called) {
      // this is a smoke test and should never actually happen
      throw new Error('once called more than once');
    } else {
      called = true;
      fun.apply(this, args);
    }
  };
}

function toPromise(func) {
  //create the function we will be returning