问题
Lets rewind to the days of cookies, ok not that far as they are old but still relevant. You can set them and read them with PHP; despite the fact they are a client side technology, you can also use JavaScript, fully client side.
Coming forward in to the future, HTML5 Local Storage, also a Client Side technology can not be set by PHP, you are solely reliant on JavaScript.
It seams as though this is the reverse way of doing it (taking away not adding). Surely to have the ability to set this data with PHP is helpful and possible somehow considering Cookies can be.
So why isn't it possible? What was the reasoning in not designing a way to do this?
Update Correct me if I am wrong, but localStorage is a replacement of Cookies, so does this not mean you are losing functionality?
回答1:
Lets rewind to the days of cookies...You can set them and read them with PHP; despite the fact they are a client side technology...
No, they aren't. Cookies are primarily a client/server technology. They were specifially designed to allow the server to send information to the client that the client will then send back to the server. From the spec:
This document defines the HTTP Cookie and Set-Cookie header fields. These header fields can be used by HTTP servers to store state (called cookies) at HTTP user agents, letting the servers maintain a stateful session over the mostly stateless HTTP protocol.
Although you can access them via client-side JavaScript, that isn't what they were created for, nor is it their sole purpose.
Web Storage (what you've called "HTML5 Local Storage") is client-side only. If you want to send that information to the server, you do it via ajax or by sending a form.
Why? That takes us into the land of speculation, but we already have cookies, whereas we didn't have a client-only way to store data prior to web storage. A client-only solution is very useful, not least because we can store a large amount of information without it being unnecessarily added to each and every HTTP request that client then makes to your server, which is a waste of bandwidth if the information is only needed client-side.
回答2:
cookies … can set them and read them with PHP; despite the fact they are a client side technology
They aren't a client side technology. They are an HTTP technology. The are embedded in the communication protocol used between the client and the server.
Local Storage is a purely client side alternative to sessions and databases, which were already available on the server side.
It's purpose is for storing data that is too big for cookies. If you could edit it on the server, then the contents would have to be sent in every request, which would be very expensive. It would also turn Local Storage into "Cookies without the restriction on size".
来源：https://stackoverflow.com/questions/21481036/why-can-cookies-be-set-by-php-nut-not-local-storage