Added keyboard navigation support and missing WAI-ARIA attributes. Tested with NVDA 2017.3 screenreader on recent major browsers.pull/127/merge
luccioman
7 years ago
parent
62c7cd9a77
commit
0b0980b364
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/*
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* Copyright (C) 2017 by luccioman; https://github.com/luccioman
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*
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* This file is part of YaCy.
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*
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* YaCy is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 2 of the License, or
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* (at your option) any later version.
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*
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* YaCy is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with YaCy. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* Add complementary features to a bar chart created with morris.js for improved accessibility :
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* keyboard navigation support and accessible labels and widget roles.
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* @param {Morris.Bar} morrisBar a bar chart created with Morris.Bar()
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* @param {String} title the accessible title to add to the bar chart
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* @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.
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* @param {String} barRole the eventual ARIA role to assign to each bar element
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* @param {Function} clickHandler an eventual click event handler function defined on the chart and to be applied when pressing "Enter" on a focused bar
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*/
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function makeAccessibleMorrisBar(morrisBar, title, barLabelGenerator, barRole, clickHandler) {
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if(morrisBar && morrisBar.el && morrisBar.el.length > 0) {
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var svgBarChart = morrisBar.el[0];
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/* Mark the chart with the appropriate ARIA roles, including fallback values for older user agents */
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svgBarChart.setAttribute("role", "graphics-document figure document");
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/* Add a comprehensive title */
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var titleElements = svgBarChart.getElementsByTagName("title");
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var titleElement;
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if(titleElements.length < 1) {
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titleElement = document.createElement("title");
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} else {
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titleElement = titleElements[0];
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}
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titleElement.innerHTML = title;
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titleElement.id = "morisBarTitle";
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svgBarChart.insertBefore(titleElement, svgBarChart.firstChild);
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svgBarChart.setAttribute("aria-labelledby", "morisBarTitle");
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/* Handle keyboard events on focusable bars to allow keyboard navigation */
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var histogramBarKeydownHandler = function(event) {
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if(event.defaultPrevented || event.altKey || event.ctrlKey || event.metaKey || event.shiftKey) {
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/* Prevent collision with any eventual other keyboard shortcuts */
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return;
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}
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if(event.key == "ArrowRight" || event.keyCode == 39) {
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var nextFocusable = this.nextSibling;
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/* Look for the next focusable bar */
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while(nextFocusable != null && (!nextFocusable.focus || !nextFocusable.hasAttribute("tabindex"))) {
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nextFocusable = nextFocusable.nextSibling;
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}
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if(nextFocusable != null && nextFocusable.focus && nextFocusable.tabIndex != null) {
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/* Set the current bar focusable but out of the tab sequence */
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this.setAttribute("tabindex", "-1")
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/* Set the next bar focusable in the tab sequence */
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nextFocusable.setAttribute("tabindex", "0");
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/* Give focus to the next bar */
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nextFocusable.focus();
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}
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} else if(event.key == "ArrowLeft" || event.keyCode == 37) {
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var prevFocusable = this.previousSibling;
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/* Look for the previous focusable bar */
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while(prevFocusable != null && (!prevFocusable.focus || !prevFocusable.hasAttribute("tabindex"))) {
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prevFocusable = prevFocusable.previousSibling;
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}
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if(prevFocusable != null && prevFocusable.focus && prevFocusable.tabIndex != null) {
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/* Set the current bar focusable but out of the tab sequence */
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this.setAttribute("tabindex", "-1");
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/* Set the next bar focusable in the tab sequence */
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prevFocusable.setAttribute("tabindex", "0");
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/* Give focus to the next bar */
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prevFocusable.focus();
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}
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} else if(clickHandler && (event.key == "Enter" || event.key == "NumpadEnter" || event.keyCode == 13)) {
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/* Find the data index from the bar position */
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var dataIndex = morrisBar.hitTest(this.x.animVal.value);
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if(dataIndex != null && dataIndex >= 0 && dataIndex < morrisBar.options.data.length) {
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/* Implement the same behavior as a link */
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clickHandler(morrisBar.options.data[dataIndex]);
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}
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}
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};
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/* When a bar receive focus from keyboard navigation : show the same toolip as the one used on mouse hover */
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var histogramBarFocusHandler = function() {
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/* Find the data index from the bar position */
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var dataIndex = morrisBar.hitTest(this.x.animVal.value);
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if(dataIndex != null && dataIndex >= 0 && morrisBar.hover != null) {
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morrisBar.hover.update.apply(morrisBar.hover, morrisBar.hoverContentForRow(dataIndex));
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}
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};
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/* When a bar looses focus : hide the tooltip */
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var histogramBarBlurHandler = function() {
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if (morrisBar.options.hideHover !== false) {
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morrisBar.hover.hide();
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}
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};
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var bars = svgBarChart.getElementsByTagName("rect");
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var data, count, bar, firstFocusableBar = true;
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for(var i = 0; i < bars.length && i < morrisBar.options.data.length; i++) {
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data = morrisBar.options.data[i];
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count = data.y;
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bar = bars[i];
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/* Only make non zero value bars focusable */
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if(count != "0") {
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/* Add the eventual bar specific role */
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if(barRole) {
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bar.setAttribute("role", barRole);
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}
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/* Add an accessible label as the regular hover is dynamically generated and this doesn't work well with screen readers */
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bar.setAttribute("aria-label", barLabelGenerator ? barLabelGenerator(data) : data.x);
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/* make each bar keyboard focusable, adding only the first one to the main tab sequence */
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bar.setAttribute("tabindex", firstFocusableBar ? "0" : "-1");
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/* Handle keyboard navigation */
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bar.onkeydown = histogramBarKeydownHandler;
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/* Show/hide each bar tooltip when each bear receive/loose focus with keyboard */
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bar.onfocus = histogramBarFocusHandler;
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bar.onblur = histogramBarBlurHandler;
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firstFocusableBar = false;
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}
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}
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}
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}
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