hellojs-xiaotian/assets/knockout/src/binding/defaultBindings/ifIfnotWith.js

A clientside Javascript library for standardizing requests to OAuth2 web services (and OAuth1 - with a shim)

// Makes a binding like with or if
function makeWithIfBinding(bindingKey, isWith, isNot, makeContextCallback) {
    ko.bindingHandlers[bindingKey] = {
        'init': function(element, valueAccessor, allBindings, viewModel, bindingContext) {
            var didDisplayOnLastUpdate,
                savedNodes;
            ko.computed(function() {
                var dataValue = ko.utils.unwrapObservable(valueAccessor()),
                    shouldDisplay = !isNot !== !dataValue, // equivalent to isNot ? !dataValue : !!dataValue
                    isFirstRender = !savedNodes,
                    needsRefresh = isFirstRender || isWith || (shouldDisplay !== didDisplayOnLastUpdate);

                if (needsRefresh) {
                    // Save a copy of the inner nodes on the initial update, but only if we have dependencies.
                    if (isFirstRender && ko.computedContext.getDependenciesCount()) {
                        savedNodes = ko.utils.cloneNodes(ko.virtualElements.childNodes(element), true /* shouldCleanNodes */);
                    }

                    if (shouldDisplay) {
                        if (!isFirstRender) {
                            ko.virtualElements.setDomNodeChildren(element, ko.utils.cloneNodes(savedNodes));
                        }
                        ko.applyBindingsToDescendants(makeContextCallback ? makeContextCallback(bindingContext, dataValue) : bindingContext, element);
                    } else {
                        ko.virtualElements.emptyNode(element);
                    }

                    didDisplayOnLastUpdate = shouldDisplay;
                }
            }, null, { disposeWhenNodeIsRemoved: element });
            return { 'controlsDescendantBindings': true };
        }
    };
    ko.expressionRewriting.bindingRewriteValidators[bindingKey] = false; // Can't rewrite control flow bindings
    ko.virtualElements.allowedBindings[bindingKey] = true;
}

// Construct the actual binding handlers
makeWithIfBinding('if');
makeWithIfBinding('ifnot', false /* isWith */, true /* isNot */);
makeWithIfBinding('with', true /* isWith */, false /* isNot */,
    function(bindingContext, dataValue) {
        return bindingContext['createChildContext'](dataValue);
    }
);