$watch, $digest, $apply

<span id="Label3"><p>$watch, $digest, $apply<br><br>$watch represents the listener of the data source, and when the data source changes, the second Parameter's callback function is triggered<br>$digest represents an event that triggers a change in the data source<br>$apply represents a package for $digest, he has one more parameter<br><br>$watch<br>The first parameter is the data source to listen to<br>The second parameter is when the listening data source has changed, triggering a callback function, the callback function contains two parameters, respectively (new value, old Value)<br><br>$digest is used to manually trigger a listener event, usually without a manual trigger, but by $apply to invoke<br><br>$apply just made $digest a package to provide manual triggering, then why do I need to manually trigger it, under normal circumstances, under angular, Modify the data source will automatically trigger, but if not in the context of angular, such as browser Dom events, SetTimeout execution, in this case, angular cannot get to the event, so, by using apply to manually trigger, in the parameters of apply to modify the data source<br><br><br>$observe, He was in the definition of directive, for the third parameter of link attr to do the monitoring<br>attr, which is actually the attribute parameter on the defined element, can be obtained by attr the parameters in the DOM<br>When the value of the parameter changes, the callback function is triggered by $observe, and unlike watch, the Listener's host object is Different.</p><p>$watch, $digest, $apply</p></span>