angular.js - How does ng automatically send a request to the background to update the page based on the value of the two-way binding?

Question

Scenario description: There is a month select drop-down box on the page. Click the drop-down box and we can select the corresponding month {code...} In the controller, we need to go to the backend to obtain the corresponding data according to the selected month {code...} I Thinking: Assume there are multiple drop-down boxes on the page, use $watch to monitor one by one...

曾经蜡笔没有小新 · Answer

Your $watch is written incorrectly:

你写成了：    $scope.$watch($scope.month, ...
应该写成：    $scope.$watch('month', ...

The following method is also very simple:

$scope.changeDo = function(){
    $http({
        url:url,
        method:'GET',
        withCredentials:true
    }).success(function(data,header,config,status){
          // do something
    });
};
$scope.$watch('year', $scope.changeDo);
$scope.$watch('month', $scope.changeDo);
$scope.$watch('day', $scope.changeDo);

If you use ng-change, the performance may be better. Remember to remove $watch() above:

The performance difference is basically negligible. I have done a similar test before, executed 1 million times, within 1 second.
If I do it, I will use the $watch method, which is convenient for maintenance later (ng-change method requires changing the controller and template, while watch method only needs to change the controller).

大家讲道理 · Answer

Drop-down boxes are generally processed using the ngChangecommand; ngChange

给我你的怀抱 · Answer

ngChange is the best choice. In principle, set as few listening queues as possible, otherwise the efficiency will be very low.