pushState: what exactly is the state object for?

Question

I've read a dozen of times now that the state object could exists of multiple key|value pairs and that it is associated with the new history entry. But could someone please give me an example of the benefits of the state object? Whats the practical use of it? I can't imagine why not just typing in {}

Answer 1

Take this small example: run fiddle (editor view):

You have a page where a user can select a color. Every time they do, we generate a new history entry:

function doPushState(color) {
    var state = {},
        title = "Page title",
        path  = "/" + color;

    history.pushState(state, title, path);
};

We leave the state object blank for now and set the URL to the color name (don't reload the page - that URL doesn't exist, so you will get a 404).

Now click on a red, green and blue once each. Note that the URL changes. Now what happens if you click the back button?

The browser does indeed go back in history, but our page doesn't notice that - the URL changes from '/blue' back to '/green', but our page stays at 'You have selected blue'. Our page has gone out of sync with the URL.

This is what the window.onpopstate event and the state object are for:

1. we include our selected color in our state object

   function doPushState(color) {
       var state = { selectedColor: color },
           title = "Page title",
           path  = "/" + color;
   
       history.pushState(state, title, path);
   };
   

2. Then we listen for the popstate event, so that we know when we have to update the selected color, which (in jQuery) is this:

   $(window).on('popstate', function(event) {
       var state = event.originalEvent.state;
   
       if (state) {
           selectColor( state.selectedColor );
       }
   });
   

Try the updated example: run fiddle (editor view): our page now updates accordingly when the user navigates back through history.

Answer 2

The most obvious example I can see for pushState, replaceState, and window.onpopstate is Ajax navigation for a site.

Say your site or web app has fixed nav & footer.. That way you can load content of new pages into a specific container, say the new <main> element.

You probably won't want to be reloading the page, and just load what you need from the new page.

Using the pushState method means you'll be able to use your browser's Back and Forward buttons to navigate, even though you're not reloading the page.

Nifty, eh?

From MDN:

HTML5 introduced the history.pushState() and history.replaceState() methods, which allow you to add and modify history entries, respectively. These methods work in conjunction with the window.onpopstate event.

Using history.pushState() changes the referrer that gets used in the HTTP header for XMLHttpRequest objects created after you change the state. The referrer will be the URL of the document whose window is this at the time of creation of the XMLHttpRequest object.

Example

There's a great example on MDN here, and the relevant Git repo here.

Answer 3

Is a specific and forward looking use case the maintenance of user view and data state in a progressive app using custom elements and templates that are divided up in the view regionally

Imagine a 64 box grid as your view, on a large screen the boxes are 147 ^2 a piece

The url represents 64/ a user ID abs related user data

The web app can then fill its grid with user specific state data

In this use case, one I fully believe is the future, the user wouldn't want to share his or her personal state and data filled view portions

By using previous history states and their related 650k of data

A whole, complex app can be, reassembled from browser history and location, including state, using a few well known sort approaches.

It's cool