When the user clicks on the button, the onclick event has been fired and the JavaScript message listed in the value of the attribute are executed.
Example
Your Name is ____. The city in which you live is ____.
<!DOCTYPE html>
<html>
<head>
<title>User Input</title>
</head>
<body>
<button id="name">Name</button>
<button id="city">City</button>
<p>
Your Name is <span id="outputName">____</span>. The city in which you live is <span id="outputCity">____</span>.
</p>
<script>
document.getElementById("name").onclick = function(){
var name = prompt("Enter your name");
document.getElementById("outputName").innerText = name;
}
document.getElementById("city").onclick = function(){
var city = prompt("Enter your city");
document.getElementById("outputCity").innerText = city;
}
</script>
</body>
</html>