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JS variable is displayed as undefined when using HTML

I am working on a project on Google Apps Script. I have a JS function that returns a date (as a text). I also have an HTML document to display a form with several inputs. I would like to prefill one input with the date returned by the JS funtion. It almost works, except it displays "undefined" instead of the date, even though I know the js funtion is working fine.
Here are some code to better understand :
The input where I call the script (don't mind the onmousemove, i just didn"t find anotherway to call the script).
<input type="text" id="deliveryDate" name="deliveryDate" onmousemove="displayActiveDate()">
So it calls the folowing script.
<script>
function displayActiveDate(){
var activeDate = google.script.run.getActiveDate();
document.getElementById("deliveryDate").value = activeDate;
}
</script>
Which in turn calls getActiveDate() which is the separate JS function that returns the date.
If you have any idea on how to solve this, I will be very thankful.

google.script.run.serverSideFunction() returns undefined. In order to get the actual response value from your serverSideFunction() you need to use the withSuccessHandler() method with a callback like so:
google.script.run.withSuccessHandler(onSuccess).serverSideFunction();
function onSuccess(data) {
// do something with the data returned by the serverSideFunction()
}
Also note that you also have withFailureHandler(err) to handle any errors you server-side functions may return.
Here is the full reference

Instead of writing document.getElementById("deliveryDate").value = activeDate; type document.getElementById("deliveryDate").innerHTML= activeDate; in your script

Laravel Mix Javascript undefined function onClick

I am using Laravels Mix feature with javascript and I am having a bit of trouble. I've made a new javascript file and included it in app.js, I've then done a function in this file. I want to call it from an onClick event however its giving me an error.
In cart.js I have an array that is adding all the products, and I also have this line of coded added.
<a onClick="removeProduct(${product["id"]})" class="btn-remove1">Remove</a>
Also in cart.js I have this function, that needs to be called on the onClick event.
function removeProduct(id) {
console.log(id);
}
However, It then gives me this error when trying to call removeProduct()
Uncaught ReferenceError: removeProduct is not defined at HTMLAnchorElement.onclick
So I'm not sure how to handle this, I guess I could use jQuery and wait for the object to be clicked and then get the id but just wondering if I can do it by onClick. Thanks for any help!
Edit:
Looking into this some more, Webpack is including Cart.js and in app.jss the function removeProduct() is there. Do I need to somehow call it like Cart.removeProduct() or something? (I've never used web pack/mix before)

I've found out with webpack you need to define it in the global scope. You can simply do that by adding this line of code.
window.removeProduct = removeProduct;

Clear your cache and then check or check that js file is included into your file or not.

Changing the value of a variable through user input and re-using it on a different page

First I would like to say that I searched and found plenty of answers and even tried a couple (more than...) but to no avail! The error is probably mine but it is time to turn to SO and ask.
Problem description: I have a variable that I want to change the value through the user input (click on btn). As soon as the user chooses the btn it will navigate to a different page that will use the result of the variable to perform certain actions. My issue is that if I alert on my 1st page I get the value being passed by the btn... But on the second page I only get "undefined"
I think it has to do with variable scope and the fact that (I think it works that way anyway) even a window.var will be deleted/purged in a different window.
Anyway, the code is something like this (on the 1st page/file):
var somAlvo;
$('#omissL').click(function(){
somAlvo = 'l';
window.location.href='index_ProofOfConcept_nivel1.html';
});
And on the "receiving end" I have the following code
<head>
...
<script type="text/javascript" src="testForm_javascript.js"></script>
to "import" the js file with the variable and:
var processo = somAlvo;
alert(processo);
I tried declaring window, not using var inside the function and so on...
This is a proof of Concept for a project in my local University, where I'm working as a research assistant (so, this is not homework ;) )
Thanks for any help/hints...

You are right in that when you navigate to another page, the entire JavaScript runtime is reset and all variables lost.
To preserve a value across page loads you have two options:
Include it as part of a query string when navigating to the new page.
Set a cookie.
You may also want to look into loading the new content through an AJAX call and replacing what is displayed. This way you won't reload the entire page which won't cause the JavaScript runtime to be reset.

JSP Parsing url and matching key words

Here is my question, I am using jsp script, trying to match a key word in requesting url and do something:
<script>
$url = '${pageContext.request.requestURL}';
if("${fn:contains(url, 'key')}" == true){
...
}
....
But this doest work... I am not sure where the problem is but I want it to be like when url contains this string, go in to the if condition.
Thank you

You are mixing JSP/EL and JavaScript as if they run in sync. This is wrong. JSP/EL runs in webserver and produces HTML code which get executed in webbrowser. JavaScript (JS) is part of the generated HTML code and runs in webbrowser only.
You need to do it either fully in JSP/EL, or fully in JavaScript. You can use JSP/EL to dynamically generate JS code which get later executed when the page arrives at browser. Rightclick page in browser, do View Source to see what JSP/EL has generated. You should not see any line of JSP/EL. You should only see HTML/JS code. It's exactly that JS code which get executed then.
You're using a JSP EL function to test a JS variable which isn't in the variable scope at that moment at all. This is not going to work. It can only test JSP/EL variables.
Here's how you could do it in pure JS:
<script>
var url = window.location.href;
if (url.indexOf('key') > -1) {
// ...
}
</script>
If you really insist in doing it using JSP/EL, you could do as follows:
<script>
var url = '${pageContext.request.requestURI}';
if (${fn:contains(pageContext.request.requestURI, 'key')}) {
// ...
}
</script>
This will then generate the following JS code (rightclick page in browser and View Source to see it):
<script>
var url = '/some/uri';
if (true) {
// ...
}
</script>
But this makes no sense. Whatever functional requirement you need to solve, you need to think twice about the right approach. Feel free to ask a new question about solving the concrete functional requirement the proper way.

If you want a parameter that the page was requested with, use ${param.paramName}. So in this case ${param.key}. See implicit objects in the docs. And if you just want to check it has a value try ${not empty param.key}.

Javascript windows.location, skipping

I have been having a strange problem with an external javascript file function skipping over windows.location. my program was supposed to take in information from forms then create validate it and after it was validated send it to a php file with get.
I simplified my code to look like
function validation(){
var alerting;//receives from forms commented out
alerting="";
var url="phpadd.php";//after this i would validate it and create the alert but all of that is commented out and irrelevant
if(alerting==""||alerting==null)
{
windows.location=url;
}
else
{
alert(alerting);
}
}
and it didn't work.
Here is the real funny thing
when I include an alert at the end after windows.location it calls the php file. When I don't it doesn't.
for instance
function validation(){
var alerting;//receives from forms commented out
alerting="";
var url="phpadd.php";//after this i would validate it and create the alert but all of that is commented out and irrelevant
if(alerting==""||alerting==null)
{//I also create the code here to put values In the url but I commented them all out so this is my effective code.
windows.location=url;
alert(url);
}
else
{
alert(alerting);
}
}
works but it has to print out the alert first. On the other hand when I don't have an alert after the windows.location call It doesn't work at all.(and I know it works with the alert because It is then redirected to the php file which I know works too). It doesn't have to be alert(url) either It could be alert anything really. in fact it did work with a while(1) loop done afterward but almost crashed the browser first. It's like it is leaving the function before it does what it is supposed to and forgetting about it.
I have tried it in firefox and in google chrome without either way working.
also if you can't find a way to do this. if you could give me a way to take in values from a form to javascript and then send valid values to a php file without windows.location(i've tried every other variant I have found also like: windows.location.href location.href location.assign(url))
I would appreciate it.
by the way The code I left out is not causing the problem because it is commented out where it doesn't work and in the one where it works that is irrelevant because it works it just puts up an alert I don't want.

You should be calling
window.location = url;
not
windows.location = url;