bindAttributeToElementScope.js

function ngBindOutToAttribute(element, attributes, attribName, scope, scopeSource, initialize) {
    var elementScope = element.scope(),
        attribField = attributes[attribName],
        valGetter = $parse(attributes[attribName]),
        valSetter = valGetter.assign,
        scopeGetter = $parse(scopeSource),
        scopeSetter = scopeGetter.assign;
    if(angular.isUndefined(scopeGetter(scope) && (angular.isUndefined(initialize) || initialize === true))) {
        scopeSetter(scope, valGetter(elementScope));
    }
    scope.$watch(scopeSource, function() {
        var useScope = elementScope;
        if(attribField.indexOf('.') < 0 && attribField.indexOf('[') < 0) {
            if(angular.isDefined(valGetter(useScope))) {
                while(angular.isUndefined(useScope[attribField])) {
                    if(useScope.__proto__ === useScope.$parent) {
                        useScope = useScope.$parent;
                    } else {
                        break;
                    }
                }
            }
        }
        valSetter(useScope, scopeGetter(scope));
        ngApply(elementScope);
    });
}