Improved accessibility of histograms widgets.

Added keyboard navigation support and missing WAI-ARIA attributes.

Tested with NVDA 2017.3 screenreader on recent major browsers.

1 files changed, 134 insertions, 0 deletions

diff --git a/htroot/js/accessibleHistogram.js b/htroot/js/accessibleHistogram.js
new file mode 100644
index 000000000..c1bfa4bdc
--- /dev/null
+++ b/htroot/js/accessibleHistogram.js
@@ -0,0 +1,134 @@
+/*    
+* Copyright (C) 2017 by luccioman; https://github.com/luccioman
+*         
+* This file is part of YaCy.
+* 
+* YaCy is free software: you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published by
+* the Free Software Foundation, either version 2 of the License, or
+* (at your option) any later version.
+* 
+* YaCy is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+* 
+* You should have received a copy of the GNU General Public License
+* along with YaCy.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+/**
+ * Add complementary features to a bar chart created with morris.js for improved accessibility : 
+ * keyboard navigation support and accessible labels and widget roles.
+ * @param {Morris.Bar} morrisBar a bar chart created with Morris.Bar()
+ * @param {String} title the accessible title to add to the bar chart
+ * @param {Function} barLabelGenerator the eventual function providing an accessible label for each bar. The function must accept one parameter (the data item related to the bar) and return a String.
+ * @param {String} barRole the eventual ARIA role to assign to each bar element
+ * @param {Function} clickHandler an eventual click event handler function defined on the chart and to be applied when pressing "Enter" on a focused bar
+ */
+function makeAccessibleMorrisBar(morrisBar, title, barLabelGenerator, barRole, clickHandler) {
+	if(morrisBar && morrisBar.el && morrisBar.el.length > 0) {
+		var svgBarChart = morrisBar.el[0];
+		/* Mark the chart with the appropriate ARIA roles, including fallback values for older user agents */
+		svgBarChart.setAttribute("role", "graphics-document figure document");
+		
+		/* Add a comprehensive title */
+		var titleElements = svgBarChart.getElementsByTagName("title");
+		var titleElement;
+		if(titleElements.length < 1) {
+			titleElement = document.createElement("title");
+		} else {
+			titleElement = titleElements[0];
+		}
+		titleElement.innerHTML = title;
+		titleElement.id = "morisBarTitle";
+		svgBarChart.insertBefore(titleElement, svgBarChart.firstChild);
+		svgBarChart.setAttribute("aria-labelledby", "morisBarTitle");
+		
+		/* Handle keyboard events on focusable bars to allow keyboard navigation */
+		var histogramBarKeydownHandler = function(event) {
+			if(event.defaultPrevented || event.altKey || event.ctrlKey || event.metaKey || event.shiftKey) {
+				/* Prevent collision with any eventual other keyboard shortcuts */
+				return;
+			}
+
+			if(event.key == "ArrowRight" || event.keyCode == 39) {
+			    	var nextFocusable = this.nextSibling;
+			    	/* Look for the next focusable bar */
+			    	while(nextFocusable != null && (!nextFocusable.focus || !nextFocusable.hasAttribute("tabindex"))) {
+			    		nextFocusable = nextFocusable.nextSibling;
+			    	}
+			    	if(nextFocusable != null && nextFocusable.focus && nextFocusable.tabIndex != null) {
+			    		/* Set the current bar focusable but out of the tab sequence */
+				    	this.setAttribute("tabindex", "-1")
+				    	/* Set the next bar focusable in the tab sequence */
+				    	nextFocusable.setAttribute("tabindex", "0");
+				    	/* Give focus to the next bar */
+				    	nextFocusable.focus();
+			    	}
+			} else if(event.key == "ArrowLeft" || event.keyCode == 37) {
+			    	var prevFocusable = this.previousSibling;
+			    	/* Look for the previous focusable bar */
+			    	while(prevFocusable != null && (!prevFocusable.focus || !prevFocusable.hasAttribute("tabindex"))) {
+			    		prevFocusable = prevFocusable.previousSibling;
+			    	}
+			    	if(prevFocusable != null && prevFocusable.focus && prevFocusable.tabIndex != null) {
+			    		/* Set the current bar focusable but out of the tab sequence */
+				    	this.setAttribute("tabindex", "-1");
+				    	/* Set the next bar focusable in the tab sequence */
+				    	prevFocusable.setAttribute("tabindex", "0");
+				    	/* Give focus to the next bar */
+				    	prevFocusable.focus();
+			    	}
+			} else if(clickHandler && (event.key == "Enter" || event.key == "NumpadEnter" || event.keyCode == 13)) {
+				/* Find the data index from the bar position */
+				var dataIndex = morrisBar.hitTest(this.x.animVal.value);
+				if(dataIndex != null && dataIndex >= 0 && dataIndex < morrisBar.options.data.length) {
+					/* Implement the same behavior as a link */
+					clickHandler(morrisBar.options.data[dataIndex]);	
+				}
+			}
+		};
+		
+		/* When a bar receive focus from keyboard navigation : show the same toolip as the one used on mouse hover */
+		var histogramBarFocusHandler = function() {
+			/* Find the data index from the bar position */
+			var dataIndex = morrisBar.hitTest(this.x.animVal.value);
+				if(dataIndex != null && dataIndex >= 0 && morrisBar.hover != null) {
+					morrisBar.hover.update.apply(morrisBar.hover, morrisBar.hoverContentForRow(dataIndex));
+				}
+		};
+		
+		/* When a bar looses focus : hide the tooltip */
+		var histogramBarBlurHandler = function() {
+		    if (morrisBar.options.hideHover !== false) {
+		    	morrisBar.hover.hide();
+		    }
+		};
+		
+		var bars = svgBarChart.getElementsByTagName("rect");
+		var data, count, bar, firstFocusableBar = true;
+		for(var i = 0; i < bars.length && i < morrisBar.options.data.length; i++) {
+			data = morrisBar.options.data[i];
+			count = data.y;
+			bar = bars[i];
+			/* Only make non zero value bars focusable */
+			if(count != "0") {
+				/* Add the eventual bar specific role */
+				if(barRole) {
+					bar.setAttribute("role", barRole);
+				}
+				/* Add an accessible label as the regular hover is dynamically generated and this doesn't work well with screen readers */
+				bar.setAttribute("aria-label", barLabelGenerator ? barLabelGenerator(data) : data.x);
+				/* make each bar keyboard focusable, adding only the first one to the main tab sequence */
+				bar.setAttribute("tabindex", firstFocusableBar ? "0" : "-1");
+				/* Handle keyboard navigation */
+				bar.onkeydown = histogramBarKeydownHandler;
+				/* Show/hide each bar tooltip when each bear receive/loose focus with keyboard */
+				bar.onfocus = histogramBarFocusHandler;
+				bar.onblur = histogramBarBlurHandler;
+				firstFocusableBar = false;
+			}
+		}
+	}
+}
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