[javascript] How do I get the Back Button to work with an AngularJS ui-router state machine?

Note

The answers that suggest using variations of $window.history.back() have all missed a crucial part of the question: How to restore the application's state to the correct state-location as the history jumps (back/forward/refresh). With that in mind; please, read on.

Yes, it is possible to have the browser back/forward (history) and refresh whilst running a pure ui-router state-machine but it takes a bit of doing.

You need several components:

• Unique URLs. The browser only enables the back/forward buttons when you change urls, so you must generate a unique url per visited state. These urls need not contain any state information though.

• A Session Service. Each generated url is correlated to a particular state so you need a way to store your url-state pairs so that you can retrieve the state information after your angular app has been restarted by back / forward or refresh clicks.

• A State History. A simple dictionary of ui-router states keyed by unique url. If you can rely on HTML5 then you can use the HTML5 History API, but if, like me, you can't then you can implement it yourself in a few lines of code (see below).

• A Location Service. Finally, you need to be able manage both ui-router state changes, triggered internally by your code, and normal browser url changes typically triggered by the user clicking browser buttons or typing stuff into the browser bar. This can all get a bit tricky because it is easy to get confused about what triggered what.

Here is my implementation of each of these requirements. I have bundled everything up into three services:

The Session Service

class SessionService

    setStorage:(key, value) ->
        json =  if value is undefined then null else JSON.stringify value
        sessionStorage.setItem key, json

    getStorage:(key)->
        JSON.parse sessionStorage.getItem key

    clear: ->
        @setStorage(key, null) for key of sessionStorage

    stateHistory:(value=null) ->
        @accessor 'stateHistory', value

    # other properties goes here

    accessor:(name, value)->
        return @getStorage name unless value?
        @setStorage name, value

angular
.module 'app.Services'
.service 'sessionService', SessionService

This is a wrapper for the javascript sessionStorage object. I have cut it down for clarity here. For a full explanation of this please see: How do I handle page refreshing with an AngularJS Single Page Application

The State History Service

class StateHistoryService
    @$inject:['sessionService']
    constructor:(@sessionService) ->

    set:(key, state)->
        history = @sessionService.stateHistory() ? {}
        history[key] = state
        @sessionService.stateHistory history

    get:(key)->
        @sessionService.stateHistory()?[key]

angular
.module 'app.Services'
.service 'stateHistoryService', StateHistoryService

The StateHistoryService looks after the storage and retrieval of historical states keyed by generated, unique urls. It is really just a convenience wrapper for a dictionary style object.

The State Location Service

class StateLocationService
    preventCall:[]
    @$inject:['$location','$state', 'stateHistoryService']
    constructor:(@location, @state, @stateHistoryService) ->

    locationChange: ->
        return if @preventCall.pop('locationChange')?
        entry = @stateHistoryService.get @location.url()
        return unless entry?
        @preventCall.push 'stateChange'
        @state.go entry.name, entry.params, {location:false}

    stateChange: ->
        return if @preventCall.pop('stateChange')?
        entry = {name: @state.current.name, params: @state.params}
        #generate your site specific, unique url here
        url = "/#{@state.params.subscriptionUrl}/#{Math.guid().substr(0,8)}"
        @stateHistoryService.set url, entry
        @preventCall.push 'locationChange'
        @location.url url

angular
.module 'app.Services'
.service 'stateLocationService', StateLocationService

The StateLocationService handles two events:

• locationChange. This is called when the browsers location is changed, typically when the back/forward/refresh button is pressed or when the app first starts or when the user types in a url. If a state for the current location.url exists in the StateHistoryService then it is used to restore the state via ui-router's $state.go.

• stateChange. This is called when you move state internally. The current state's name and params are stored in the StateHistoryService keyed by a generated url. This generated url can be anything you want, it may or may not identify the state in a human readable way. In my case I am using a state param plus a randomly generated sequence of digits derived from a guid (see foot for the guid generator snippet). The generated url is displayed in the browser bar and, crucially, added to the browser's internal history stack using @location.url url. Its adding the url to the browser's history stack that enables the forward / back buttons.

The big problem with this technique is that calling @location.url url in the stateChange method will trigger the $locationChangeSuccess event and so call the locationChange method. Equally calling the @state.go from locationChange will trigger the $stateChangeSuccess event and so the stateChange method. This gets very confusing and messes up the browser history no end.

The solution is very simple. You can see the preventCall array being used as a stack (pop and push). Each time one of the methods is called it prevents the other method being called one-time-only. This technique does not interfere with the correct triggering of the $ events and keeps everything straight.

Now all we need to do is call the HistoryService methods at the appropriate time in the state transition life-cycle. This is done in the AngularJS Apps .run method, like this:

Angular app.run

angular
.module 'app', ['ui.router']
.run ($rootScope, stateLocationService) ->

    $rootScope.$on '$stateChangeSuccess', (event, toState, toParams) ->
        stateLocationService.stateChange()

    $rootScope.$on '$locationChangeSuccess', ->
        stateLocationService.locationChange()

Generate a Guid

Math.guid = ->
    s4 = -> Math.floor((1 + Math.random()) * 0x10000).toString(16).substring(1)
    "#{s4()}#{s4()}-#{s4()}-#{s4()}-#{s4()}-#{s4()}#{s4()}#{s4()}"

With all this in place, the forward / back buttons and the refresh button all work as expected.