Javascript AngularJs函数表达式中的参数

我正在看“组件树示例”一节中的示例。我对传递给组件树不同级别中的函数的参数感到困惑

    <hero-detail ng-repeat="hero in $ctrl.list" hero="hero" 
on-delete="$ctrl.deleteHero(hero)" on-update="$ctrl.updateHero(hero, prop, value)"></hero-detail>

function HeroDetailController() {
         var ctrl = this;
         ctrl.delete = function() {
           ctrl.onDelete({hero: ctrl.hero});
    };
   
    
   
    ctrl.update = function(prop, value) {
       ctrl.onUpdate({hero: ctrl.hero, prop: prop, value: value});
     };
   }
   
   angular.module('heroApp').component('heroDetail', {
     templateUrl: 'heroDetail.html',
     controller: HeroDetailController,
     bindings: {
       hero: '<',
       onDelete: '&',
       onUpdate: '&'
     }
   });