$watch and $apply

1. When you use Ng-model, Ng-repeat, and so on to bind the value of an element, AngularJS creates a $watch for that value, as long as the value changes in the range of AngularJS, and all places are updated synchronously. While you are writing custom directive, you need to define your own $watch to implement this automatic synchronization.

2, sometimes you change the value of the model in the code, the view is not updated, which is often encountered in custom event binding. You will need to manually invoke scope. $apply () to trigger an interface update. This is illustrated in the example above DatePicker. Third-party plug-ins may have call back, and we can also write the callback function as an anonymous function as a parameter in $apply ().

$watch and $apply