angular-optimistic-cache

Optimistically use cached data before a request finishes.

The problem

Usually you have something like this in your Angular.JS application:

angular.module('myApp').controller('PeopleCtrl', function ($scope, $http) {
    $http.get('/api/people').then(function (result) {
        $scope.people = result.data;
    });
});

<ul>
    <li ng-repeat="person in people">{{person.name}}</li>
</ul>

This simple example is a page that will fetch a list of people from the backend and shows it on a page.

Unfortunately, it suffers from the "uncomfortable silence". Here's a diagram to explain:

When you arrive on the page, it'll first show a blank page. After some time, this gets swapped with the data. Your app feels fast because navigation between screens is instant, but it feels jarring.

This is especially annoying when switching back-and-forth between pages, as it happens every time.

A similar thing happens when going from the list to a detail page:

Isn't it a bit strange that you know the name of the person on which the user clicked, but upon navigation that suddenly gets lost, forcing us to wait until all the info is loaded? Why not start out with showing the name while the rest of the data loads?

The angular-optimistic-cache module is a very lightweight module to add some of that to your application. It's probably the least intrustive way to avoid uncomfortable silences.

Installation

Add angular-optimistic-cache to your project:

bower install --save angular-optimistic-cache

Add it to your HTML file:

<script src="bower_components/angular-optimistic-cache/dist/angular-optimistic-cache.min.js"></script>

Reference it as a dependency for your app module:

angular.module('myApp', ['rt.optimisticcache']);

How it works

This module works by wrapping the promises that you wait for. It adds a toScope method where you can indicate where the result should be placed on the scope.

It then does the following:

• The promise is loaded as usual, in the background.
• If it has a previously-cached value for the promise, it'll put that one on the scope.
• Once the promise is loaded, it replaces the scope value with the up-to-date data.

The end result: users see data instantly, which is updated once it's loaded.

Usage

Let's take another look at the controller in the example above:

angular.module('myApp').controller('PeopleCtrl', function ($scope, $http) {
    $http.get('/api/people').then(function (result) {
        $scope.people = result.data;
    });
});

First split out the loading function:

angular.module('myApp').controller('PeopleCtrl', function ($scope, $http) {
    function fetchPeople() {
        return $http.get('/api/people').then(function (result) {
            return result.data;
        });
    }
    
    fetchPeople().then(function (people) {
        $scope.people = people;
    });
});

Then wrap the promise:

angular.module('myApp').controller('PeopleCtrl', function ($scope, $http, optimisticCache) {
    function fetchPeople() {
        var promise = $http.get('/api/people').then(function (result) {
            return result.data;
        });
        return optimisticCache(promise, '/api/people');
    }
    
    fetchPeople().then(function (people) {
        $scope.people = people;
    });
});

Now change the usage:

angular.module('myApp').controller('PeopleCtrl', function ($scope, $http, optimisticCache) {
    function fetchPeople() {
        var promise = $http.get('/api/people').then(function (result) {
            return result.data;
        });
        return optimisticCache(promise, '/api/people');
    }
    
    fetchPeople().toScope($scope, 'people');
});

And magic will happen!

API

The module exposes one service: optimisticCache(promise, namespace, options).

Parameters:

• A promise (any promise, doesn't have to be related to $http). This promise will be wrapped and augmented with the toScope method.
• A namespace that represents where the loaded data is situated. This doesn't have to be an existing URL. It's used to match multiple calls together.
• Optional extra options (see below).

Master / detail

The namespace is how calls are matched: when a promise is created, a cache is checked to see if a previous promise with the same namespace parameter has existed. If that's the case, the previous result is temporarily put on the scope (this avoids the uncomfortable silence).

Namespaces are structured and the module assumes that you use standard REST structures. This means that the element in /api/people with an id of 123 should map to /api/people/123. When a promise is resolved with an array, the cache will also be filled for children.

An example (namespace: /api/people):

[
    { id: 123, name: "Test" }
]

This also fills the cache of namespace /api/people/123 with { id: 123, name: "Test" }.

Options

The options parameter is an optional object that can have the following keys (all are optional):

• idField (default: id): Which field to use for populating child caches.
• populateChildren (default: true): Whether or not to populate child caches if the promise results to an array.

License

(The MIT License)

Copyright (C) 2014 by Ruben Vermeersch <[e-mail]>

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.