Can you explain how Angular is able to locate the directives on a webpage and establish connections with or observe those elements?
I've searched through the DOM reference, but it seems like methods like getElementbySomething and querySelectorAll may not be sufficient for identifying an Angular directive.
The resources I found only talk about the listeners that are provided as arguments to $scope.$watch. So, how do the directives determine when to trigger $apply and initiate the digest cycle?
Angular doesn't actively search for directives. Upon initialization, Angular processes each element on the page to check if it contains a registered directive. This process is known as the compile phase.
During this phase, the compile function is called for each directive on the element based on priority order, and Angular stores the element associated with that directive for future reference.
Regarding your query about using $apply, it's only necessary when an external force alters a scope value outside of the Angular lifecycle. This typically occurs when binding to a standard event like 'click' within the directive itself.
If you're looking for a directive using querySelector, try this approach:
var desiredDirective = document.querySelector('[ng-repeat]');
To access the value of a directive, use the following method:
console.log(desiredDirective.attributes['ng-repeat'].value)
Any changes within the directive are monitored and observed. These changes should ideally stay within Angular's scope. If you need to alter them using plain JavaScript, why is that so?
You can continuously check the value using an interval. Check out this CodePen example: http://codepen.io/rias/pen/bdNgJe?editors=101
var value = 0;
function incrementValue() {
value += 1;
document.getElementById('changeme').attributes['ng-example-directive'].value = value;
}
// Simulating Angular watching for external changes
(function() {
var targetDirective = document.querySelector('[ng-example-directive]');
var pollValue = targetDirective.attributes['ng-example-directive'].value;
// Polling for changes
setInterval(function() {
var newValue = targetDirective.attributes['ng-example-directive'].value;
if (newValue != pollValue) {
pollValue = newValue;
alert(pollValue);
}
}, 100);
}());
<body ng-app>
<section ng-example-directive="1" id="changeme">
<button onclick="incrementValue()">Increase Value</button>
</section>
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