Is it possible to conditionally apply transclution to directive? - angularjs

Question

Is it possible to decide whether to apply transclusion to an element based on a scope variable ?
For example ( Stupid simplified reduced example of what i'm trying to achieve )
app.directive('myHighlight', function () {
return {
transclude : true,
template : "<div style='border:1px solid red'><span ng-transclude></span></div>"
}
});
app.directive('myDirective', function () {
return {
template : "<span>some text</span>",
link : function (scope,element,attr) {
if ( 'shouldHighlight' in attr) {
// wrap this directive with my-highlight
}
}
}
});
And then in the html
<span my-directive></span>
<span my-directive should-highlight></span>
Note, please don't tell me to just add the highlight instead of should-highlight, as i said this is a dumb reduced example. Thanks.

Answer 1

Instead of optionally applying the highlight directive, always apply it and do the optional wrapping inside that directive. The optional wrapping is achieved with an ng-if and a boolean passed from myDirective to myHighlight via markup:
<div my-highlight="someBooleanValue">some text</div>
The myHighlight template:
<div ng-if="actuallyTransclude" style="border:1px solid red">
<span ng-transclude></span>
</div>
<div ng-if="!actuallyTransclude" ng-transclude></div>
Working jsfiddle: http://jsfiddle.net/wilsonjonash/X6eB5/

Answer 2

Sure. When you specify the transclude option, you know that you can declaratively indicate where the content should go using ng-transclude.
In the linking function of the directive, you will also get a reference to a transclude function (https://docs.angularjs.org/api/ng/service/$compile, see link section):
function link(scope, iElement, iAttrs, controller, transcludeFn) { ... }
The transcludeFn will return the transcluded content, so you can conditionally insert that were and when you want to in the link function of your directive.
Example (http://jsfiddle.net/DKLY9/22/)
HTML
<parentdir flg="1">
Child Content
</parentdir>
JS
app.directive('parentdir', function(){
return {
restrict : 'AE',
scope: {
flg : "="
},
transclude : true,
template : "<div>Parent {{childContent}} Content</div>",
link : function(scope, elem, attr, ctrl, transcludeFn){
if (scope.flg==1){
scope.childContent="Include Me instead";
}
else {
scope.childContent = transcludeFn()[0].textContent;
}
}
}
});
This is a simplified example. To get a better idea of how to use the transclude function, refer to the following : http://blog.omkarpatil.com/2012/11/transclude-in-angularjs.html

Answer 3

When I approach these kind of problems I just look at what angular did. Usually their source code is very readable and easy to re-use. ngTransclude is no different:
https://github.com/angular/angular.js/blob/master/src/ng/directive/ngTransclude.js
I leave the rest to you. You can either create your own transclusion directive that receives also a condition, or just duplicate the code into your specific directive when the if condition is true.
If you still have trouble, please let me know and we'll set up a plunker.