Created: 2012-03-20 15:16
Updated: 2015-10-13 13:10

NeXML JavaScript libraries

The JavaScript libraries use the badgerfish mapping of (Ne)XML onto JSON. The nexml.js library wraps around such JSON objects and exposes them with getters (no setters, though you can poke around the JSON data structure anyway if you must update it). Example usage is shown in jsonlib/nexml-js.html

Library design

The library is a single file but it uses JavaScript mix-ins quite extensively. If you were to draw an inheritance tree of these mix-ins and child classes it would mirror the classes in the NeXML schema.

The library is used by instantiating a document object, like so:

var doc = new NeXML.Document(json);

Where json is a badgerfish mapping of a valid NeXML document, i.e. a JSON data structure. What then happens is that a cascade of constructors springs into action to decorate the appropriate parts of the JSON tree as JavaScript classes. For example, each otu structure in JSON becomes accessible as an instance of the OTU class in the library, with all the behaviours of that class, and its 'superclasses', in this case Base and Labeled (which, transitively, may have 'superclasses' as well).

To understand how this is implemented in the library, the var statements for variables that start with capital letters such as var Labeled declare mix-ins/roles/something akin to superclasses in the form of Object declarations whose properties serve as method names and values as functions. JavaScript's object model is a bit different (being charitably, here) so this is the way in which the library approximates the behaviour that programmers in more orthodox object-oriented languages might expect.

The Object properties and values (i.e. the methods) are attached to child instances in their constructors by copying over the properties and values of named superclasses using the copyFields function call. Because this child instance might wrap data structures of different types (i.e. Array, Object or scalar) the function normalizeList is then called in order to correctly invoke constructors for these data.

Example data files

  • nexml-trees.js - is the equivalent of the file trees.xml in the 'core' repository of NeXML files. It demonstrates tree and network structures.
  • nexml-characters.js - is the equivalent of the file characters.xml in the 'core' repository of NeXML files. It demonstrates character state matrices.

Example browser demo

  • nexml-js.html - an HTML file that shows how data can be accessed and displayed in a browser.
  • json2.js - a 3rd party JavaScript file (public domain) that the demo uses to serialize JSON to text with JSON.stringify.
  • nexml2html.css - a simple CSS stylesheet that the demo needed to make it super pretty.

There is also the file nexml2html.js, which once upon a time featured in a browser demo. It's not used now as such but it shows how to access metadata annotations using CURIEs, which is a pretty useful feature.

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