How do I pre populate a simple html form with html5 and javascript?

As with any site, you might want to employ the help of a library. LocalStorage unfortunately isn't supported across every browsers and libraries that deal with it often fall back (if they can) to using age old cookies, automatically. They can also tell you if your code will work at all by informing you what the library detects (the ability to use local storage or cookies, etc).

An existing library that supports this and is very simple to use, including IE 7/6 polyfils, is store.js:

https://github.com/marcuswestin/store.js

e.g. // most important, check if it even works! if (!store.enabled) { alert('You have no local storage support here '); } // Store 'firstname' (just shortening the form access code, season to taste) store.set('firstname', document.getElementById('firstname').value); // Get 'firstname' document.getElementById('firstname').value = store.get('firstname'); // Remove 'firstname', maybe after submit store.remove('firstname'); // clear it all store.clear();

The examples there are pretty self explanatory and there's plenty of them.