How to make an alert if the user inputs nothing else.

Question

if the user doesn't input anything then how to make alert in js.

Answer 1

function hello(){
var input=prompt("enter your name");
if(input===""){
alert("enter a valid name");
}
else{
document.write("hi "+input);
}
}

Answer 2

why js use
<input type="text" name="whatever" required>
i wont be able to submit until wrote anything into it

Answer 3

but to answere your question
alert("whaterver you wanna alert him to do");