AngularJS：指令监视属性表达式

Question

I want a directive to watch the result of an attribute expression such as:

<div scroll-if="test === selectedTest"></div>

So that it can then react to the change and scroll to the particular element. I seem to be struggling to find out how I can watch for changes to that expression.

Answer 1

Use $watch :

app.directive('scrollIf', function() {
  return {
    restrict: 'A',
    link: function(scope, element, attributes) {

      var actionScroll = function(newVal, oldVal) {
        if(newVal!==oldVal) {
          console.log("scrolling");
        }
      }

      scope.$watch(attributes.scrollIf, actionScroll);
    }
  }
});

$watch can evaluate the attribute expression scroll-if , the actionScroll listener will run if this expression is true.

Is necessary to add the condition newVal!==oldVal , because actionScroll always runs the first time. This is explained in the $watch documentation