Support local file Data Sources

[Frencil]

The Problem

Presently LocusZoom does not support creating a data source that maps to a local file. This is a likely use case for the plugin on a longer time scale.

It's unclear exactly how to approach this problem without having some example files to work with. The HTML5 File API will likely play a part.

Opportunities

In scope for this feature we may want to consider generating a few small "example" data files that live in the repository. These would be very useful for building automated tests against local file data sources logic (see #36, related).

From there we could also strike the current data sources from the demo and define a proper DefaultDataSources object (in keeping with the pattern of DefaultLayout and DefaultState). In this way the "hello world" for the LocusZoom plugin could literally be a one-liner (that is, one line of JavaScript logic to call populate and the HTML to include the scripts and create an empty div).

[Frencil]

Update: upon further discussion while we would still benefit from a DefaultDataSources object it would be more practical to have this be populated with reliable statgen API endpoints.

[Frencil]

2017 Update

This is an older issue but it still holds that LocusZoom.js lacks an obvious approach to working with local files. However, it's not impossible:

apiBase = window.location.origin + window.location.pathname.substr(0, window.location.pathname.length - "demo.html".length) + "staticdata/";
data_sources = new LocusZoom.DataSources()
    .add("assoc", ["AssociationLZ", {url: apiBase + "assoc_10_114550452-115067678.json?", params: {analysis: 3, id_field: "variant"}}])
    .add("ld", ["LDLZ", { url: apiBase + "ld_10_114550452-115067678.json?" }])
    .add("gene", ["GeneLZ", { url: apiBase + "genes_10_114550452-115067678.json?" }])
    .add("recomb", ["RecombLZ", { url: apiBase + "recomb_10_114550452-115067678.json?" }])
    .add("constraint", ["GeneConstraintLZ", {  url: apiBase + "constraint_10_114550452-115067678.json?" }]);

As of v0.5.6 this approach is demonstrated in index.html using local files.

While this is demonstrated in the repo currently it's not clear that it's there. This issue is resolved when this is documented in the README in the repo as well as on the wiki.

[Frencil]

Update: README and Wiki updated, repo example tuned up. Good enough for now!