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))
}

can you provide an example how to use it?

usage:

waitForLocalStorage('coolProperty', function (value) {
  console.log('coolProperty', value);
});

the 3rd argument isn't necessary.

Actually you can use something like this.
https://stackoverflow.com/a/42922083

not working

The issue with the original gist is the following:

if (!localStorage.getItem(key)) return (timer = setTimeout(waitForLocalStorage.bind(null, key), 100))

Fix:

waitForLocalStorage.bind(null, key, cb )

The callback is undefined after the recursion if we don't pass it over

Thanks @moimikey for the useful snippet - sometimes we "don't know" when a local storage item becomes available, it could be set by a separate component async for example

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.