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Liferay 7: Using URL params and Javascript to prefill a form

I've been working with Liferay 7 for a while and needed to create a feedback form with prefilled values. I created a feedback form and a page, where it's shown and where I could add Javascript.
The user clicks on a link ("Did you find this helpful? Yes/No") and it takes you to the feedback page with the page and answer as URL parameters.
URL: {feedback-page-url/} ?pageUrl=/services&answer=Yes
Now here's where the problems began. Liferay updates it's values very confusingly and while generic document.getElementsByName(...) etc. seemed to work at first, they updated back when clicking the page. The difficult thing is to update the right values in right elements, so they won't be overrun by Liferay.
I provided an answer to my question below. Feel free to ask me anything, I'll try to help :)

Full code block in the end!
So I found out a solution to this problem. Liferay creates an instance (_com_liferay...) and uses it's values to be up to date, so we need to get a hold of it and update it's values. You can do it manually by inspecting and finding your instance, but I have an automatic code that should get it for you.
The id we are searching for is for DDMFormPortlet and the String we get this way is close to perfect. The String that document.querySelector() finds begins with p_p_id_com..., so we can use .substring to remove the unnecessary part and then add +"form" in the end to make it complete. If you find a better way to find this, please share it :)
// _com_liferay_dynamic_data_mapping_form_web_portlet_DDMFormPortlet_INSTANCE_randomkey_form
const idFinder = function() {
const idString = document.querySelector('[id*="DDMFormPortlet"]').id;
return(idString.substring(6) + "form");
}
Now that we have the correct String text, we'll find the element, that corresponds to it:
const formFieldArray = window[idFinder()];
Now if you try it just by itself, it most likely won't find anything, because it's loads slowly. I put all of this into try-catch with setTimeout() to make sure everything works as intended. Now all we need to do is collect the information from our URL and set it to the correct places.
const params = new URLSearchParams(location.search);
const formAutoFiller = function (params) {
try {
const formFieldArray = window[idFinder()];
// make sure you have the numbers according to your form!
formFieldArray.pages[0].rows[0].columns[0].fields[0].value=params.get('pageUrl');
formFieldArray.pages[0].rows[1].columns[0].fields[0].value=params.get('answer');
// ...
}
}
And finally, as the changed values update to the form after clicking an input field, we'll move the selection focus to one of the input fields after the other code is ran:
document.getElementsByClassName("ddm-field-text")[1].focus();
A bit cleanup for myself and we're done! Full Javascript here:
const params = new URLSearchParams(location.search);
const idFinder = function() {
const idString = document.querySelector('[id*="DDMFormPortlet"]').id;
return(idString.substring(6) + "form");
}
const formAutoFiller = function (params) {
try {
const formFieldRows = window[idFinder()].pages[0].rows;
formFieldRows[0].columns[0].fields[0].value=params.get('pageUrl');
formFieldRows[1].columns[0].fields[0].value=params.get('answer');
document.getElementsByClassName("ddm-field-text")[1].focus();
} catch (e) {
setTimeout(formAutoFiller, 500, params);
}
}
formAutoFiller(params);

setting a variable in javascript to be used in another form

I have form with a Grid (telerik), i think the technology behind it doesnt matter. I let user click on a row in the grid. During the click I extract a value from the Grid with Javascript, like so:
function RadDrillDoubleClick(sender, eventArgs) {
var Code = eventArgs.getDataKeyValue("Status");
if (Code == "In Progress" || Code == "")
{
location.href = "Main1.aspx?mode=edit&DID=" + eventArgs.getDataKeyValue("D_ID");
}
else {
location.href = "Main1.aspx?mode=view&DID=" + eventArgs.getDataKeyValue("D_ID");
}
}
After user has clicked the grid, I call this JS function and send them to correct .aspx page with either VIEW or EDIT mode dependent directly on the Code.
What I'm trying to do is once I get to the Main1.aspx page, I want to be able to continue to hold the CODE value, because when users performs a certain action, I'll need to call a javascript function and use the actual CODE to determine what the user will be able to do.....
var Code = eventArgs.getDataKeyValue("Status");
is there any way I can somehow create like a GLOBAL Variable called
CodeValue
that I can pass around to another form without doing it in the URL?

When the browser navigates to a page, all current JavaScript is unloaded from the browser. This means any functions/variables, etc. will not be accessible on the new page unless you've persisted the value in some way.
Common ways of persisting the value include:
Add it to the query string of the URL the user is navigating to
Save the value to a cookie
Save the value to local/session storage
For your scenario, #1 is probably your best bet (keep in mind the user can have multiple browsers/tabs open to your site).

One way to get the value from URL is like this: on the page Main1.aspx, you add to your JavaScript a function that will run after page loads and that will get what it needs from the current URL
var globalValue; // variable that will receive the value from URL
window.onload = function() {
var thisURL = window.location.href;
globalValue = url.split("?").pop();
// this will store in globalValue everything that comes after the last "?"
// example: if the url is www.site.com/text?value, it will store string "value" to globalValue
};

How to make a Global Variable with User Input?

I am making a program where I have a user input where the user types in their cat's name, and then I want the name to appear in the text throughout the program. Here is my code, it is in Javascript:
var catName = getText("nameInput");
onEvent("startBtn", "click", function(event) {
setScreen("feedingScreen");
setText("feedingText", catName+" is hungry! Give "+catName+" some food!
Click fish to feed.");
});
Whwn I run this program, however, the cat name does not appear in the text. How can I make it where the text does show up?

If the catName variable is going to be used for a long time, I'd consider using localStorage to store it and retrieve it whenever I want (even when the user leaves the page and comes back).
Example :
function setCatName(name) {
window.localStorage.setItem('catName', name);
}
function getCatName() {
return window.localStorage.getItem('catName');
}
If you don't want that though, you could store it in the window object. Take note that it's considered bad practice (but so are global variables in general).
Example :
function setCatName(name) {
window.catName = name;
}
function getCatName() {
return window.catName;
}
UPDATE :
It's funny because the examples on Mozilla's Docs use localStorage to set and retrieve a cat's name too :
localStorage documentation

xpages href computed in javascript

I have an <a> tag which I'm using to redirect the user to another xpage.
Its href property is:
<a target="_blank" href="http://serv/MyBase.nsf">
I use a simple view listing a doc. which contains the server and the name of the application.
So, I want to use some #DbLookup function in javascript to get into 2 var the above server and app name:
var server = #Unique(#DbColumn(#DbName(), "myVw", 1);
var name = #Unique(#DbColumn(#DbName(), "myVw", 2);
var concat = server+"/"+name;
return concat;
How can I compute the href property to return the concat variable?

Create a Link control xp:link and calculate the URL in attribute value:
<xp:this.value><![CDATA[#{javascript:var server .... }]]></xp:this.value>

Knut's approach is correct, but your code isn't :-). For every XPages load (or refresh) you do 4 #DbLookup. You can do a set of optimisations here:
Combine the result you want in the view itself, so you only need one lookup
Cache the value in the session (or application scope)
something like this (add nice error handling):
if (sessionScope.myHref) {
// Actually do nothing here
} else {
sessionScope.myHref = #Unique(#DbColumn(#DbName(), "myVw", 3);
}
return sessionScope.myHref;
The 3rd column would have the concatenation in the view already. That little snippet does a lookup only once per session. If it is the same for all users, use the applicationScope then it is even less.

Variable not updating in script string, yet it updates

Very confused here.
I have a search box which reads a list of school names from my database. When I select a school, the id (from the db) gets put in a hidden textbox.
I also have a search box which reads a list of courses from my database. However, I made the query so that it only reads the courses from the selected school.
It does that, in theory.
I was planning to pass the school id, which I grab from the hidden box, to the search script which in turn passes it to my database query. However, the variable I put my school id in doesn't seem to be updating.. yet it does. Let me explain.
I come on the page. The school for my test account has id 1. The id number in my hidden box is indeed 1. I search for a school which I know has some courses assigned to it: the id number in the box changes to 3.
I have a JS variable called school_id which I declared outside of my $(document).ready. I assume that means it's global (that's what I got taught even though SO told me once it isn't really the correct way to do this. Still have to look into that). I wrote a function which updates this variable when the school search box loses focus:
$("#school").blur(function() {
school_id = $("#school_id").val();
});
A quick javascript:alert(school_id); in my browser bar also shows the updated variable: it is now 3 instead of 1.
Onto the search script part of my page (excerpt of the script):
script:"/profiel/search_richting?json=true&limit=6&id=" + school_id + "&"
As you can see, I pass the school_id variable to the script here. However, what seems to be happening is that it always passes '1', the default variable when the page loads. It simply ignores the updated variable. Does this string get parsed when the page loads? In other words, as soon as the page loads, does it actually say &id=1? That's the only idea I can come up with why it would always pass '1'.
Is there a way to make this variable update in my script string? Or what would be the best way to solve this? I'm probably missing out on something very simple here again, as usual. Thanks a lot.
EDIT
Updated per request. I added a function getTheString as was suggest and I use the value of this function to get the URL. Still doesn't work though, it still seems to be concatenating before I get a chance to update the var. HOWEVER, with this code, my ajax log says id:[object HTMLInputElement], instead of id:1. Not sure what that means.
<script type="text/javascript">
var school_id;
$(document).ready(function() {
$("#school").blur(function() {
school_id = $("#school_id").val();
});
// zoekfunctie
var scholen = {
script:"/profiel/search_school?json=true&limit=6&",
varname:"input",
json:true,
shownoresults:false,
maxresults:6,
callback: function (obj) { document.getElementById('school_id').value = obj.id; }
};
var as_json = new bsn.AutoSuggest('school', scholen);
var richtingen = {
script: getTheString(),
varname:"input",
json:true,
shownoresults:true,
maxresults:6
};
var as_json2 = new bsn.AutoSuggest('studierichting', richtingen);
});
function getTheString() {
return "/profiel/search_richting?json=true&limit=6&id=" + school_id + "&";
}
</script>

This is because the URL is static, it is not updated as the ID changes.
You should update the URL as part of the code you wrote to get the ID:
$("#school").blur(function() {
school_id = $("#school_id").val();
// update URL here ...
});

Aren't you concatenating script:"/profiel/search_richting?json=true&limit=6&id=" + school_id + "&" before the event is fired and the var updated?

Okay. So the problem was my third party plug-in instead of the code I wrote. I fixed this by editing the code of the autoSuggest plugin so it now includes my id field in the AJAX request.
var url = this.oP.script+this.oP.varname+"="+encodeURIComponent(this.sInp)+"&id="+ $("#school_id").val();
Thanks to everyone who tried to help me out!