I'm trying to create a web app, and I need to know the user input from form.
<form action="" method="get" class="settings">
<div class="settings">
<label for="length">length of character(s): </label>
<input type="number" name="length" id="length" placeholder="5" required>
<input type="submit" value="Change">
</div>
</form>I need the form to run a js func foo() so I assume that I need to put it
<form action="" method="get" class="settings">
↑how do I get the value of id="length" and use it in form action"foo()"?
You can get the value of length with document.getElementById("id").value;
In order to run a js from form, you need to use onsubmit="" instead of action=""
onsubmit="" allows you to execute a js function upon submission of the form, while action="" allows you to be redirected to another page/site upon submission.
Read more about action="" in this site
Here is a workable code based on your example
function foo(){
var lgt = document.getElementById("length").value;
alert(lgt);
}<form class="settings" onsubmit="foo()">
<div class="settings">
<label for="length">length of character(s): </label>
<input type="number" name="length" id="length" placeholder="5" required>
<input type="submit" value="Change">
</div>
</form>