snappymail/vendors/knockout/src/components/customElements.js

(function (undefined) {
    // Overridable API for determining which component name applies to a given node. By overriding this,
    // you can for example map specific tagNames to components that are not preregistered.
    ko.components['getComponentNameForNode'] = function(node) {
        var tagNameLower = ko.utils.tagNameLower(node);
        if (ko.components.isRegistered(tagNameLower)) {
            // Try to determine that this node can be considered a *custom* element; see https://github.com/knockout/knockout/issues/1603
            if (tagNameLower.indexOf('-') != -1 || ('' + node) == "[object HTMLUnknownElement]") {
                return tagNameLower;
            }
        }
    };

    ko.components.addBindingsForCustomElement = function(allBindings, node, bindingContext, valueAccessors) {
        // Determine if it's really a custom element matching a component
        if (node.nodeType === 1) {
            var componentName = ko.components['getComponentNameForNode'](node);
            if (componentName) {
                // It does represent a component, so add a component binding for it
                allBindings = allBindings || {};

                if (allBindings['component']) {
                    // Avoid silently overwriting some other 'component' binding that may already be on the element
                    throw new Error('Cannot use the "component" binding on a custom element matching a component');
                }

                var componentBindingValue = { 'name': componentName, 'params': getComponentParamsFromCustomElement(node, bindingContext) };

                allBindings['component'] = valueAccessors
                    ? function() { return componentBindingValue; }
                    : componentBindingValue;
            }
        }

        return allBindings;
    }

    var nativeBindingProviderInstance = new ko.bindingProvider();

    function getComponentParamsFromCustomElement(elem, bindingContext) {
        var paramsAttribute = elem.getAttribute('params');

        if (paramsAttribute) {
            var params = nativeBindingProviderInstance['parseBindingsString'](paramsAttribute, bindingContext, elem, { 'valueAccessors': true, 'bindingParams': true }),
                rawParamComputedValues = ko.utils.objectMap(params, function(paramValue, paramName) {
                    return ko.computed(paramValue, null, { disposeWhenNodeIsRemoved: elem });
                }),
                result = ko.utils.objectMap(rawParamComputedValues, function(paramValueComputed, paramName) {
                    var paramValue = paramValueComputed.peek();
                    // Does the evaluation of the parameter value unwrap any observables?
                    if (!paramValueComputed.isActive()) {
                        // No it doesn't, so there's no need for any computed wrapper. Just pass through the supplied value directly.
                        // Example: "someVal: firstName, age: 123" (whether or not firstName is an observable/computed)
                        return paramValue;
                    } else {
                        // Yes it does. Supply a computed property that unwraps both the outer (binding expression)
                        // level of observability, and any inner (resulting model value) level of observability.
                        // This means the component doesn't have to worry about multiple unwrapping. If the value is a
                        // writable observable, the computed will also be writable and pass the value on to the observable.
                        return ko.computed({
                            'read': function() {
                                return ko.utils.unwrapObservable(paramValueComputed());
                            },
                            'write': ko.isWriteableObservable(paramValue) && function(value) {
                                paramValueComputed()(value);
                            },
                            disposeWhenNodeIsRemoved: elem
                        });
                    }
                });

            // Give access to the raw computeds, as long as that wouldn't overwrite any custom param also called '$raw'
            // This is in case the developer wants to react to outer (binding) observability separately from inner
            // (model value) observability, or in case the model value observable has subobservables.
            if (!Object.prototype.hasOwnProperty.call(result, '$raw')) {
                result['$raw'] = rawParamComputedValues;
            }

            return result;
        } else {
            // For consistency, absence of a "params" attribute is treated the same as the presence of
            // any empty one. Otherwise component viewmodels need special code to check whether or not
            // 'params' or 'params.$raw' is null/undefined before reading subproperties, which is annoying.
            return { '$raw': {} };
        }
    }
})();