Run HTML conversion in web worker thread

[nerk]

Investigate if HTML conversion can be performed in web worker thread to avoid blocking of editor UI events during conversion.

[mojavelinux]

Great idea!

[nerk]

Got it working with a quick hack as follows.

In main.js:

var converter = new Worker('converter.js'); // may be constructed only once

// structure to pass docText, options, and attributes. Opal hash won't work 
var data = {
    docText: docText,
    basedir: basedir,
    pwd: FileUtils.getDirectoryPath(window.location.href),
    attributes: attributes
};

converter.postMessage(data);
converter.onmessage = function (e) {

    var bodyText = e.data;
    // add header, footer etc.
    htmlSource = ... + bodyText + ...;
    // update view
    $iframe.attr("srcdoc", htmlSource);
};

All code doing the conversion is in self-contained, separate file 'converter.js'. No access to console, DOM, document, or window objects.

// converter.js

// Fake console, Opal needs it.

var console = {
    log: function(m) { // Create HTML and prepend to generated output? ...},
    warn: function(m) {// something ...}
};

===> include opal.js code
===> include asciidoctor.js code 

var onmessage = function (e) {
    postMessage(convert(e.data));
}

// data must contain all options and attributes, can't pass Opal.hash2
function convert(data) {

    Opal.ENV['$[]=']("PWD", data.pwd);
    var opts = Opal.hash2(['base_dir', 'safe', 'doctype', 'attributes'], {
                'base_dir': data.basedir,
                'safe': 'safe',
                'doctype': 'article',
                'attributes': data.attributes
            });

    return Opal.Asciidoctor.$convert(data.docText, opts);
}

Smooth editing!

converter.js could be made usable for other projects requiring background conversion. Either a separate build step is needed to create this single file from its parts, or the build process for Asciidoctor.js could create and distribute such a combined file with a proper interface.

[nerk]

Implemented for version 1.0.4