Friday, 15 November 2019

AngularJS Directive for Focus trap for modal popups

If you use Bootstrap modal popup, chances are that hitting TAB enough types on the keyboard will navigate out of the modal popup and back to the background web page, the DOM elements "beneath" the modal popup. This AngularJS directive should fix up that, wrapping everything in an IFE (Immediately invoking Function Expression). Note that this only works if your module is called 'app' (the default name).

(function() {
angular.module('app')
 .directive('modal', trapFocus)
 
 function trapFocus() {
        return {
            restrict: 'C',
            priority: 1,
            link: function (scope, element, attr) {
                if (typeof (scope.registerFocusTrap) === 'undefined') {
                    scope.registerFocusTrap = registerFocusTrap;
                } else {
                    for (var i = 0; i < element.length; i++) {
                        registerFocusTrap(element.get(i));
 
                    }
                }
 
            }
        };
    }
 
    function registerFocusTrap(element) {
        var focusableEls = element.querySelectorAll(
            'a[href]:not([disabled]), button:not([disabled]), textarea:not([disabled]), input[type="text"]:not([disabled]), input[type="radio"]:not([disabled]), input[type="checkbox"]:not([disabled]), select:not([disabled])');
        var firstFocusableEl = focusableEls[0];
        var lastFocusableEl = focusableEls[focusableEls.length - 1];
        // ReSharper disable once InconsistentNaming
        var KEYCODE_TAB = 9;
 
        $(element).on('keydown',
            function (e) {
                console.log('inside registerFocusTrap keydown');
                var isTabPressed = (e.key === 'Tab' || e.keyCode === KEYCODE_TAB);
 
                if (!isTabPressed) {
                    return;
                }
 
                if (e.shiftKey) /* shift + tab */ {
                    if (document.activeElement === firstFocusableEl) {
                        lastFocusableEl.focus();
                        e.preventDefault();
                    }
                } else /* tab */ {
                    if (document.activeElement === lastFocusableEl) {
                        firstFocusableEl.focus();
                        e.preventDefault();
                    }
                }
            }
        );
    }
  
}); 
 

Note that the name of registered modules in AngularJs is not supported in AngularJs by itself. This polyfill should tough fix up this.

(function(orig) {
    angular.modules = [];
    angular.module = function() {
        if (arguments.length > 1) {
            angular.modules.push(arguments[0]);
        }
        return orig.apply(null, arguments);
    }
})(angular.module);

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