A common thing you will end up having to do is get some input from a user - a password, a filename, a search query, etc.
If you don't have or need access to CGI scripting, JavaScript may be sufficient for your needs.
Give me a number < 100 to play with:That may look like a regular form but isn't. Typically, when you see something like that with a 'Submit' button, it triggers a script on a server, which then executes.
In the case here, the action when submitted is a JavaScript function run locally.
The text entry and button is some simple HTML with a JavaScript function tied to it when clicked. The response is displayed in an HTML div. View the source code to see that.
function DoMath() {
const NumIn = document.getElementById('UserIn').value;
if (NumIn >= 100) {
document.getElementById('NumOut').innerHTML = 'Nope. Too BIG';
}
else {
if (NumIn < 100) {
let NumOut = Math.pow(NumIn,3) // cube the user entry
document.getElementById('NumOut').innerHTML = NumIn+'<sup>3</sup>: '+NumOut;
}
}
}