How to add HTML Div onClick eventListener() [duplicate]

I am learning to create a calculator using Javascript. I have added my HTML elements and CSS style but I am struggling to make the eventListener work.

I have the following code (just a sample), and I have styled HTML with using grid:

HTML:

<div id="frame">
        <div class="btn">1</div>
        <div class="btn">2</div>
        <div class="btn">3</div>
</div>

JavaScript:

document.querySelectorAll(".btn").addEventListener("click", btnClick);

function btnClick(){
    alert("hi");
}

Desired outcome: Alert “Hi” whenever I click on any of the div

From everything I have learned, I thought this code should give me the desired outcome but I thought wrong. I would really appreciate if someone could point out the fault.

Many Thanks in Advance!!