angular-attachFocusFunction.js

const angular = require("angular");

angular
  .module("modulename")
  .directive('attachFocusFunction', function($parse) {
    return {
      scope: false,
      link(scope, element, attributes) {
        let expr = $parse(attributes.attachFocusFunction);
        if(!expr.assign){
          throw "Please provide a valid lhs expression for the attachFocusFunction";
        }

        expr.assign(scope, function() {
          element[0].focus();
        });
      }
    }
  });

<!-- in component's html template -->
<input type="text" attach-focus-function="$ctrl.setFocus" />

// in component's controller
this.setFocus();