DOM Ready

Espere hasta que el DOM esté listo antes de ejecutar el código.

  
  let ready = function(fn) {

    // Sanity check
    if(typeof fn !== 'function') return;

    // If document is already loaded, run method
    if(document.readyState === 'interactive' || document.readyState === 'complete') {
      return fn();
    }

    // Otherwise, wait until document is loaded
    document.addEventListener( 'DOMContentLoaded', fn, false );
  };

  ready(function() {
      console.log('Run code');
  });