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You can use addEventListener to listen for a particular event on an HTML element and execute a JavaScript function as a response. To create an alert box, you can use the following code:

HTML:

<button id="myButton">Click me</button>

JavaScript:

const myButton = document.getElementById("myButton");

myButton.addEventListener("click", showAlert);

function showAlert() {
  alert("Hello, world!");
}

In this example, we select the HTML button element with the ID "myButton" using document.getElementById(). We then attach an event listener to this button using addEventListener(). The first argument is the event to listen for ("click" in this case), and the second argument is the function to execute when the event is triggered.

The function showAlert() simply displays an alert box with a message. When the user clicks the button, the showAlert() function is executed, and the alert box pops up.