why is setInterval doing a loop?

Question

This is an html page with some simple javascript. The alert pops up again and again after clicking the ok button. I don't understand. I can see setInterval runs the function after 3 seconds pass. The alert pops up I close the alert so that should be the end. I clicked on the "Try it" button only once. If there is a loop I don't see it.
// This is the code with the loop in question.
<button onclick="myFunction()">Try it</button>
<script>
var myVar;
function myFunction() {
myVar = setInterval(alertFunc, 3000);
}
function alertFunc() {
alert("Hello!");
}
</script>

Answer 1

setTimeout(function, milliseconds)
Executes a function, after waiting a specified number of milliseconds.
setInterval(function, milliseconds)
Same as setTimeout(), but repeats the execution of the function continuously.

Answer 2

https://www.w3schools.com/jsref/met_win_setinterval.asp
setInterval is the loop.
setInterval repeats the the function every x milliseconds until clearInterval is called.
You want setTimeout