fa20-bt/plugin/markdown/markdown.js

/**
 * The reveal.js markdown plugin. Handles parsing of
 * markdown inside of presentations as well as loading
 * of external markdown documents.
 */
(function(){

	if( typeof marked === 'undefined' ) {
		throw 'The reveal.js Markdown plugin requires marked to be loaded';
	}

	if( typeof hljs !== 'undefined' ) {
		marked.setOptions({
			highlight: function( lang, code ) {
				return hljs.highlightAuto( lang, code ).value;
			}
		});
	}

	/**
	 * Retrieves the markdown contents of a slide section
	 * element. Normalizes leading tabs/whitespace.
	 */
	function getMarkdownFromSlide( section ) {

		var template = section.querySelector( 'script' );

		// strip leading whitespace so it isn't evaluated as code
		var text = ( template || section ).textContent;

		var leadingWs = text.match( /^\n?(\s*)/ )[1].length,
			leadingTabs = text.match( /^\n?(\t*)/ )[1].length;

		if( leadingTabs > 0 ) {
			text = text.replace( new RegExp('\\n?\\t{' + leadingTabs + '}','g'), '\n' );
		}
		else if( leadingWs > 1 ) {
			text = text.replace( new RegExp('\\n? {' + leadingWs + '}','g'), '\n' );
		}

		return text;

	}

	/**
	 * Given a markdown slide section element, this will
	 * return all arguments that aren't related to markdown
	 * parsing. Used to forward any other user-defined arguments
	 * to the output markdown slide.
	 */
	function getForwardedAttributes( section ) {

		var attributes = section.attributes;
		var result = [];

		for( var i = 0, len = attributes.length; i < len; i++ ) {
			var name = attributes[i].name,
				value = attributes[i].value;

			// disregard attributes that are used for markdown loading/parsing
			if( /data\-(markdown|separator|vertical|notes)/gi.test( name ) ) continue;

			if( value ) {
				result.push( name + '=' + value );
			}
			else {
				result.push( name );
			}
		}

		return result.join( ' ' );

	}

	/**
	 * Helper function for constructing a markdown slide.
	 */
	function createMarkdownSlide( data ) {

		var content = data.content || data;

		if( data.notes ) {
			content += '<aside class="notes" data-markdown>' + data.notes + '</aside>';
		}

		return '<script type="text/template">' + content + '</script>';

	}

	/**
	 * Parses a data string into multiple slides based
	 * on the passed in separator arguments.
	 */
	function slidifyMarkdown( markdown, options ) {

		options = options || {};
		options.separator = options.separator || '^\n---\n$';
		options.notesSeparator = options.notesSeparator || 'note:';
		options.attributes = options.attributes || '';

		var separatorRegex = new RegExp( options.separator + ( options.verticalSeparator ? '|' + options.verticalSeparator : '' ), 'mg' ),
			horizontalSeparatorRegex = new RegExp( options.separator ),
			notesSeparatorRegex = new RegExp( options.notesSeparator, 'mgi' );

		var matches,
			noteMatch,
			lastIndex = 0,
			isHorizontal,
			wasHorizontal = true,
			content,
			notes,
			slide,
			sectionStack = [];

		// iterate until all blocks between separators are stacked up
		while( matches = separatorRegex.exec( markdown ) ) {
			notes = null;

			// determine direction (horizontal by default)
			isHorizontal = horizontalSeparatorRegex.test( matches[0] );

			if( !isHorizontal && wasHorizontal ) {
				// create vertical stack
				sectionStack.push( [] );
			}

			// pluck slide content from markdown input
			content = markdown.substring( lastIndex, matches.index );
			noteMatch = content.split( notesSeparatorRegex );

			if( noteMatch.length === 2 ) {
				content = noteMatch[0];
				notes = noteMatch[1].trim();
			}

			slide = {
				content: content,
				notes: notes || ''
			};

			if( isHorizontal && wasHorizontal ) {
				// add to horizontal stack
				sectionStack.push( slide );
			}
			else {
				// add to vertical stack
				sectionStack[sectionStack.length-1].push( slide );
			}

			lastIndex = separatorRegex.lastIndex;
			wasHorizontal = isHorizontal;
		}

		// add the remaining slide
		( wasHorizontal ? sectionStack : sectionStack[sectionStack.length-1] ).push( markdown.substring( lastIndex ) );

		var markdownSections = '';

		// flatten the hierarchical stack, and insert <section data-markdown> tags
		for( var i = 0, len = sectionStack.length; i < len; i++ ) {
			// vertical
			if( sectionStack[i].propertyIsEnumerable( length ) && typeof sectionStack[i].splice === 'function' ) {
				markdownSections += '<section '+ options.attributes +'>' +
										'<section data-markdown>' +  sectionStack[i].map( createMarkdownSlide ).join( '</section><section data-markdown>' ) + '</section>' +
									'</section>';
			}
			else {
				markdownSections += '<section '+ options.attributes +' data-markdown>' + createMarkdownSlide( sectionStack[i] ) + '</section>';
			}
		}

		return markdownSections;

	}

	function loadExternalMarkdown() {

		var sections = document.querySelectorAll( '[data-markdown]'),
			section;

		for( var i = 0, len = sections.length; i < len; i++ ) {

			section = sections[i];

			if( section.getAttribute( 'data-markdown' ).length ) {

				var xhr = new XMLHttpRequest(),
					url = section.getAttribute( 'data-markdown' );

				datacharset = section.getAttribute( 'data-charset' );

				// see https://developer.mozilla.org/en-US/docs/Web/API/element.getAttribute#Notes
				if( datacharset != null && datacharset != '' ) {
					xhr.overrideMimeType( 'text/html; charset=' + datacharset );
				}

				xhr.onreadystatechange = function() {
					if( xhr.readyState === 4 ) {
						if ( xhr.status >= 200 && xhr.status < 300 ) {

							section.outerHTML = slidifyMarkdown( xhr.responseText, {
								separator: section.getAttribute( 'data-separator' ),
								verticalSeparator: section.getAttribute( 'data-vertical' ),
								notesSeparator: section.getAttribute( 'data-notes' ),
								attributes: getForwardedAttributes( section )
							});

						}
						else {

							section.outerHTML = '<section data-state="alert">' +
								'ERROR: The attempt to fetch ' + url + ' failed with HTTP status ' + xhr.status + '.' +
								'Check your browser\'s JavaScript console for more details.' +
								'<p>Remember that you need to serve the presentation HTML from a HTTP server.</p>' +
								'</section>';

						}
					}
				};

				xhr.open( 'GET', url, false );

				try {
					xhr.send();
				}
				catch ( e ) {
					alert( 'Failed to get the Markdown file ' + url + '. Make sure that the presentation and the file are served by a HTTP server and the file can be found there. ' + e );
				}

			}
			else if( section.getAttribute( 'data-separator' ) ) {

				section.outerHTML = slidifyMarkdown( getMarkdownFromSlide( section ), {
					separator: section.getAttribute( 'data-separator' ),
					verticalSeparator: section.getAttribute( 'data-vertical' ),
					notesSeparator: section.getAttribute( 'data-notes' ),
					attributes: getForwardedAttributes( section )
				});

			}
		}

	}

	function convertMarkdownToHTML() {

		var sections = document.querySelectorAll( '[data-markdown]');

		for( var i = 0, len = sections.length; i < len; i++ ) {

			var section = sections[i];

			var notes = section.querySelector( 'aside.notes' );
			var markdown = getMarkdownFromSlide( section );

			section.innerHTML = marked( markdown );

			// If there were notes, we need to re-add them after
			// having overwritten the section's HTML
			if( notes ) {
				section.appendChild( notes );
			}

		}

	}

	loadExternalMarkdown();
	convertMarkdownToHTML();

})();