I have created a custom popup with the popupTemplate function with ArcGIS JS API 4.x

And i add a button in popup content by html.

but i can not addEventListener to a button in popup.

here is the way i am try to do now: ((the full code is here:https://codepen.io/llllllllc/pen/mdpabGw))

1. return html to create button in popup content

const popupTemplate = {
                // autocasts as new PopupTemplate()
                title: "Population in {NAME}",
                content: populationChange,
                };

                layer.popupTemplate = popupTemplate;

                function populationChange(feature) 
                {
                    const div = document.createElement("div");
                    div.innerHTML =
                        "<input type='button' id='btn' value='CLICK'>";
                    return div;
                }

2. watch content change

view.popup.watch("content", (newValue, oldValue, propertyName, target) => {......});

3.querySelector("#btn") then addEventListener but it fail ,and console.log(btn) show btn is null

const btn = document.querySelector("#btn");
console.log(btn)
btn.addEventListener(
    "click",
    function () {
        lert("HELLO WORLD!");
    },
   false
);

the consol show like this picture

Any help much appreciated!!!