var hasfocusUpdatingProperty = '__ko_hasfocusUpdating';
ko.bindingHandlers['hasfocus'] = {
    'init': function(element, valueAccessor, allBindingsAccessor) {
        var handleElementFocusChange = function(isFocused) {
            // Where possible, ignore which event was raised and determine focus state using activeElement,
            // as this avoids phantom focus/blur events raised when changing tabs in modern browsers.
            // However, not all KO-targeted browsers (Firefox 2) support activeElement. For those browsers,
            // prevent a loss of focus when changing tabs/windows by setting a flag that prevents hasfocus
            // from calling 'blur()' on the element when it loses focus.
            // Discussion at https://github.com/SteveSanderson/knockout/pull/352
            element[hasfocusUpdatingProperty] = true;
            var ownerDoc = element.ownerDocument;
            if ("activeElement" in ownerDoc) {
                isFocused = (ownerDoc.activeElement === element);
            }
            var modelValue = valueAccessor();
            ko.expressionRewriting.writeValueToProperty(modelValue, allBindingsAccessor, 'hasfocus', isFocused, true);
            element[hasfocusUpdatingProperty] = false;
        };
        var handleElementFocusIn = handleElementFocusChange.bind(null, true);
        var handleElementFocusOut = handleElementFocusChange.bind(null, false);

        ko.utils.registerEventHandler(element, "focus", handleElementFocusIn);
        ko.utils.registerEventHandler(element, "focusin", handleElementFocusIn); // For IE
        ko.utils.registerEventHandler(element, "blur",  handleElementFocusOut);
        ko.utils.registerEventHandler(element, "focusout",  handleElementFocusOut); // For IE
    },
    'update': function(element, valueAccessor) {
        var value = ko.utils.unwrapObservable(valueAccessor());
        if (!element[hasfocusUpdatingProperty]) {
            value ? element.focus() : element.blur();
            ko.dependencyDetection.ignore(ko.utils.triggerEvent, null, [element, value ? "focusin" : "focusout"]); // For IE, which doesn't reliably fire "focus" or "blur" events synchronously
        }
    }
};

var hasfocusUpdatingProperty = '__ko_hasfocusUpdating';
var hasfocusLastValue = '__ko_hasfocusLastValue';
ko.bindingHandlers['hasfocus'] = {
    'init': function(element, valueAccessor, allBindingsAccessor) {
        var handleElementFocusChange = function(isFocused) {
            // Where possible, ignore which event was raised and determine focus state using activeElement,
            // as this avoids phantom focus/blur events raised when changing tabs in modern browsers.
            // However, not all KO-targeted browsers (Firefox 2) support activeElement. For those browsers,
            // prevent a loss of focus when changing tabs/windows by setting a flag that prevents hasfocus
            // from calling 'blur()' on the element when it loses focus.
            // Discussion at https://github.com/SteveSanderson/knockout/pull/352
            element[hasfocusUpdatingProperty] = true;
            var ownerDoc = element.ownerDocument;
            if ("activeElement" in ownerDoc) {
                isFocused = (ownerDoc.activeElement === element);
            }
            var modelValue = valueAccessor();
            ko.expressionRewriting.writeValueToProperty(modelValue, allBindingsAccessor, 'hasfocus', isFocused, true);

            //cache the latest value, so we can avoid unnecessarily calling focus/blur in the update function
            element[hasfocusLastValue] = isFocused;
            element[hasfocusUpdatingProperty] = false;
        };
        var handleElementFocusIn = handleElementFocusChange.bind(null, true);
        var handleElementFocusOut = handleElementFocusChange.bind(null, false);

        ko.utils.registerEventHandler(element, "focus", handleElementFocusIn);
        ko.utils.registerEventHandler(element, "focusin", handleElementFocusIn); // For IE
        ko.utils.registerEventHandler(element, "blur",  handleElementFocusOut);
        ko.utils.registerEventHandler(element, "focusout",  handleElementFocusOut); // For IE
    },
    'update': function(element, valueAccessor) {
        var value = !!ko.utils.unwrapObservable(valueAccessor()); //force boolean to compare with last value
        if (!element[hasfocusUpdatingProperty] && element[hasfocusLastValue] !== value) {
            value ? element.focus() : element.blur();
            ko.dependencyDetection.ignore(ko.utils.triggerEvent, null, [element, value ? "focusin" : "focusout"]); // For IE, which doesn't reliably fire "focus" or "blur" events synchronously
        }
    }
};

Fix for #698. Keep track of latest focus value, so we don't unnecessarily call focus/blur in the update function.