wait-for-localstorage.js

/**
 * Michael Scott Hertzberg <mshertzberg@gmail.com> (http://hertzber.gs)
 * 
 * recursively check for set localStorage value every 100ms.
 * this will also safely clear the timeout once found.
 * can be used callback style or directly.
 * functionally pure.
 */
function waitForLocalStorage(key, cb, timer) {
  if (!localStorage.getItem(key)) return (timer = setTimeout(waitForLocalStorage.bind(null, key, cb), 100))
  clearTimeout(timer)
  if (typeof cb !== 'function') return localStorage.getItem(key)
  return cb(localStorage.getItem(key))
}

correct gist following @dragGH102 's fix:

function waitForLocalStorage(key, cb, timer) {
	if ( ! localStorage.getItem( key ) ) {
		return timer = setTimeout(
			waitForLocalStorage.bind( null, key, cb ),
			100
		)
	}
	clearTimeout( timer )
	if ( typeof cb !== 'function' ) {
		return localStorage.getItem( key )
	}
	return cb( localStorage.getItem( key ) )
}

@dragGH102 thanks! good catch! gist has been updated.