YUI Library Examples: Focus Manager Node Plugin: Accessible Menu Button

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Focus Manager Node Plugin: Accessible Menu Button

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Setting Up the HTML

+For a menu button, start with an <a> element whose +href attribute is set to the id of an <div> +that wraps a list of <input> elements. +Therefore, without JavaScript and CSS, the menu button is simply an in-page +link to a set of additional buttons. +

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Progressive Enhancement

+The markup above will be transformed into a menu button widget using both CSS +and JavaScript. To account for the scenario where the user has CSS enabled in +their browser but JavaScript is disabled, the CSS used to style the menu button +will be loaded via JavaScript using the +built-in loader of the YUI Global Object. +Additionally, JavaScript will be used to temporarily hide the menu button markup +while the JavaScript and CSS are in the process of loading to prevent the user +from seeing a flash unstyled content. +

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ARIA Support

+Through the use of CSS and JavaScript the HTML for the menu button can be +transformed into something that looks and behaves like a desktop menu button, +but users of screen readers won't perceive it as an atomic widget, but rather +simply as a set of HTML elements. However, through the application +of the +WAI-ARIA Roles and States, it is +possible to improve the semantics of the markup such that users of screen +readers perceive it as a menu button control. +

+ + +

Keyboard Functionality

+The keyboard functionality for the button's menu will be provided by the Focus +Manager Node Plugin. The Focus Manager's +descendants +attribute is set to a value of "input", so that only one menuitem in the +button's menu is in the browser's default tab flow. This allows users +navigating via the keyboard to use the tab key to quickly move into and out of +the menu. Once the menu has focus, the user can move focus among each menuitem +using the up and down arrows keys, as defined by the value of the +keys +attribute. The +focusClass +attribute is used to apply a class of yui-menuitem-active to +the parent <li> of each +<input> when it is focused, making it easy to style the +menuitem's focused state in each of the +A-Grade browsers. + ++YUI({ + base:"../../build/", + timeout: 10000, + modules: { + "menubutton-css": { + type: "css", + fullpath: "assets/menubutton.css" + } + } + +}).use("menubutton-css", "node-focusmanager", "node-event-simulate", "overlay", function(Y) { + + var menuButton = Y.Node.get("#button-1"), + menu; + + + var initMenu = function () { + + menu = new Y.Overlay({ + contentBox: "#menu-1", + visible: false, + tabIndex: null + }); + + menu.render(); + + + Y.Node.get("#menu-1").setStyle("display", ""); + + var boundingBox = menu.get("boundingBox"), + contentBox = menu.get("contentBox"); + + boundingBox.addClass("yui-buttonmenu"); + contentBox.addClass("yui-buttonmenu-content"); + + + // Append a decorator element to the bounding box to render the shadow. + + boundingBox.appendChild(Y.Node.create('<div class="yui-menu-shadow"></div>')); + + + // Apply the ARIA roles, states and properties to the menu. + + boundingBox.setAttrs({ + role: "menu", + "aria-labelledby": menuButton.get("id") + }); + + boundingBox.queryAll("input").set("role", "menuitem"); + + + // For NVDA: Add the role of "presentation" to each LI + // element to prevent NVDA from announcing the + // "listitem" role. + + boundingBox.queryAll("div,ul,li").set("role", "presentation"); + + + // Use the FocusManager Node Plugin to manage the focusability + // of each menuitem in the menu. + + contentBox.plug(Y.Plugin.NodeFocusManager, { + + descendants: "input", + keys: { next: "down:40", // Down arrow + previous: "down:38" }, // Up arrow + focusClass: { + className: "yui-menuitem-active", + fn: function (node) { + return node.get("parentNode"); + } + }, + circular: true + + }); + + + // Subscribe to the change event for the "focused" attribute + // to listen for when the menu initially gains focus, and + // when the menu has lost focus completely. + + contentBox.focusManager.after("focusedChange", function (event) { + + if (!event.newVal) { // The menu has lost focus + + // Set the "activeDescendant" attribute to 0 when the + // menu is hidden so that the user can tab from the + // button to the first item in the menu the next time + // the menu is made visible. + + this.set("activeDescendant", 0); + + } + + }); + + + // Hide the button's menu if the user presses the escape key + // while focused either on the button or its menu. + + Y.on("key", function () { + + menu.hide(); + menuButton.focus(); + + }, [menuButton, boundingBox] ,"down:27"); + + + if (Y.UA.ie === 6) { + + // Set the width and height of the menu's bounding box - + // this is necessary for IE 6 so that the CSS for the + // shadow element can simply set the shadow's width and + // height to 100% to ensure that dimensions of the shadow + // are always sync'd to the that of its parent menu. + + menu.on("visibleChange", function (event) { + + if (event.newVal) { + + boundingBox.setStyles({ height: "", width: "" }); + + boundingBox.setStyles({ + height: (boundingBox.get("offsetHeight") + "px"), + width: (boundingBox.get("offsetWidth") + "px") }); + + } + + }); + + } + + + menu.after("visibleChange", function (event) { + + var bVisible = event.newVal; + + // Focus the first item when the menu is made visible + // to allow users to navigate the menu via the keyboard + + if (bVisible) { + + // Need to set focus via a timer for Webkit and Opera + Y.Lang.later(0, contentBox.focusManager, contentBox.focusManager.focus); + + } + + boundingBox.set("aria-hidden", (!bVisible)); + + }); + + + // Hide the menu when one of menu items is clicked. + + Y.on("delegate", function (event) { + + var oTarget = event.currentTarget; + + alert("You clicked " + oTarget.query("input").get("value")); + + contentBox.focusManager.blur(); + menu.hide(); + + }, boundingBox, "click", "li"); + + + // Focus each menuitem as the user moves the mouse over + // the menu. + + Y.on("mouseenter", function (event) { + + var focusManager = contentBox.focusManager; + + if (focusManager.get("focused")) { + focusManager.focus(event.currentTarget.query("input")); + } + + }, boundingBox, "li"); + + + // Hide the menu if the user clicks outside of it or if the + // user doesn't click on the button + + boundingBox.get("ownerDocument").on("mousedown", function (event) { + + var oTarget = event.currentTarget; + + if (!oTarget.compareTo(menuButton) && + !menuButton.contains(oTarget) && + !oTarget.compareTo(boundingBox) && + !boundingBox.contains(oTarget)) { + + menu.hide(); + + } + + }); + + }; + + + menuButton.addClass("yui-menubutton"); + + + // Hide the list until it is transformed into a menu + + Y.Node.get("#menu-1").setStyle("display", "none"); + + + // Remove the "yui-loading" class from the documentElement + // now that the necessary YUI dependencies are loaded. + + menuButton.get("ownerDocument").get("documentElement").removeClass("yui-loading"); + + + // Apply the ARIA roles, states and properties to the anchor. + + menuButton.setAttrs({ + role: "button", + "aria-haspopup": true + }); + + + // Remove the "href" attribute from the anchor element to + // prevent JAWS and NVDA from reading the value of the "href" + // attribute when the anchor is focused. + + if ((Y.UA.gecko || Y.UA.ie) && navigator.userAgent.indexOf("Windows") > -1) { + + menuButton.removeAttribute("href"); + + // Since the anchor's "href" attribute has been removed, the + // element will not fire the click event in Firefox when the + // user presses the enter key. To fix this, dispatch the + // "click" event to the anchor when the user presses the + // enter key. + + Y.on("key", function (event) { + + event.currentTarget.simulate("click"); + + }, menuButton, "down:13"); + + } + + + // Set the "tabIndex" attribute of the anchor element to 0 to + // place it in the browser's default tab flow. This is + // necessary since 1) anchor elements are not in the default + // tab flow in Opera and 2) removing the "href" attribute + // prevents the anchor from firing its "click" event + // in Firefox. + + menuButton.set("tabIndex", 0); + + + var showMenu = function (event) { + + // For performance: Defer the creation of the menu until + // the first time the button is clicked. + + if (!menu) { + initMenu(); + } + + + if (!menu.get("visible")) { + + menu.set("align", { + node: menuButton, + points: [Y.WidgetPositionExt.TL, Y.WidgetPositionExt.BL] + }); + + menu.show(); + + } + + // Prevent the anchor element from being focused + // when the users mouses down on it. + event.preventDefault(); + + }; + + + // Bind both a "mousedown" and "click" event listener to + // ensure the button's menu can be invoked using both the + // mouse and the keyboard. + + menuButton.on("mousedown", showMenu); + menuButton.on("click", showMenu); + +}); + +

YUI Library Examples: Focus Manager Node Plugin: Accessible Menu Button

Focus Manager Node Plugin: Accessible Menu Button

Setting Up the HTML

Progressive Enhancement

ARIA Support

Keyboard Functionality

+ Focus Manager Node Plugin Examples:

More Focus Manager Node Plugin Resources: