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How to ignore invalid URL parameters?

Before I go on, let me say that I've looked through a number of threads already and can't find an answer that works for me.
Basically, I've built a custom link shortener and I'm using URLSearchParams to pull the URL to be shortened and the custom slug from the URL search query as follows:
var e = window.location.search;
const urlParams = new URLSearchParams(e);
const url = urlParams.get("url");
const slug = urlParams.get("slug");
Where the format for a query is: ?url=https://google.com&slug=customslug
After the parameters are handled, the URL string is treated with trim() to remove any whitespace. The final output is encoded with encodeURIComponent() when the API I'm using (https://short.io) is called.
However, I want to be able to pass URLs with &, like so: ?url=https://google.com/&testing&slug=customslug. My ideal solution would simply treat any & that isn't part of the &slug parameter as a part of the URL contained within the &url parameter. Currently, the & character is ignored if it isn't attached to a valid parameter (url or slug).
I have tried encoding the query input using encodeURIComponent(), but that results in a failure to pick up on either defined parameter. I have also tried splitting the input using split("&slug",1), but that results in an array and I cannot pass arrays to the Short.io API.
Any suggestions?

You should use the URL Encoded ampersand symbol %26.
var e = "?url=https://google.com/%26testing&slug=customslug";
const urlParams = new URLSearchParams(e);
const url = urlParams.get("url");
const slug = urlParams.get("slug");
console.log(url);
console.log(slug);

I solved my issue by building off of #CherryDT's comment about using window.location.hash to get my URL string. Ultimately, I chose to forgo the idea of a slug in the address bar, since it would cause further problems with my script.
While this solution is only applicable for my purposes, I'm detailing the solution because it functions as a workaround for the issue of not being able to encode a passed URL string from the address bar. Might be useful to someone, someday.
var e = window.location.href.replace(window.location.hash, '');
if (e.endsWith("?") === true) {
var url = window.location.hash.substr(1);
if (url === "") {
// Error code
} else {
console.log("A URL to be shortened was provided via hash.");
// Pass url to rest of script
}
}

How can I insert dynamic value to URL in cy.visit()?

I am trying to insert value to URL which I want to visit. I use this (for example):
const idp = '10'
cy.visit('http://test.com/aaa/bbb?id=${idp}')
but when I run this, it will ends on this http://test.com/aaa/bbb?id=$%7Bidp%7D
instead of id=10.
Also I am interested how can I get value from URL to variable.
For example I have URL http://test.com/aaa/bbb?id=5 and I want to create variable idc which will have value 5.

I think you are using the wrong quotes, you need to use backticks to use Template Literals:
cy.visit(`http://test.com/aaa/bbb?id=${idp}`)
You can then use cy.url() to get the current URL as a string and use JavaScript to parse the string as normal.

For the first part of your question you need to use backticks(also called grave accents) as outlined in the Template Literals docs instead of regular quotes. Your line would then look like -
cy.visit(`http://test.com/aaa/bbb?id=${idp}`)
For the second part of your question, you can use URLSearchParams (Note this DOES NOT work in IE). An example would be -
var url = new URL("http://test.com/aaa/bbb?id=5");
var searchParams = new URLSearchParams(url.search);
const urlParams = new URLSearchParams(searchParams );
const myParam = urlParams .get('id');

Trying to parse special characters to retrieve JSON element in JavaScript

I need help on a university project I am working on with NodeRed. I am integrating a JSON API in JS (NodeRed) and hit a roadblock. Here's the kind of JSON I'm retrieving:
{"#SpeciesCode":"NO2","#MeasurementDateGMT":"2016-04-04 00:00:00","#Value":"58.2"}
That "#" sign is really giving me all sorts of troubles because wether I use JSON.parse or stringify or escaping, it is either telling me " Unexpected token #" or just "undefined value".
Here is the code I'm working with:
var body = msg.payload;
var bodyParsed = JSON.parse(body);
var data = bodyParsed.AirQualityData.Data;
var valueStr="#Value";
var value=JSON.stringify(valueStr);
var valueParsed=JSON.parse(value);
var element = data[0].valueParsed;
return {payload:element};
If you want to have a go at it, here's the URL to the data: http://api.erg.kcl.ac.uk/AirQuality/Data/Site/SiteCode=WM6/StartDate=2016-04-04/EndDate=2016-05-04/Json
[UPDATE: SOLVED] Thanks to jcubic who provided the solution in the comments below:
to access property using a variable you need to use bracket notation:
var element = data[0][valueParsed]; also you don't need to stringify and parse #value just use data[0]["#Value"]
So the new code is
var body = msg.payload;
var bodyParsed = JSON.parse(body);
var data = bodyParsed.AirQualityData.Data;
var element = data[0]["#Value"];
return {payload:element};

Does string contain Ajax?

I am writing a tutorial page for JavaScript and to prevent xss I want to check if the user's input contains any ajax and if it does return an error string. Also any other elements that could be used for xss in the input should make it error. What would the code for this be?

Try defining a RegExp including methods, strings which should not pass validation , utilize RegExp.prototype.test() with string as argument
var re = /XMLHttpRequest|.\.ajax|.\.get|.\.post|.\.getScript|script/;
var str = "$.post";
var res = re.test(str) ? new Error("error") : str;
console.log(res)

Creating a new Location object in javascript

Is it possible to create a new Location object in javascript? I have a url as a string and I would like to leverage what javascript already provides to gain access to the different parts of it.
Here's an example of what I'm talking about (I know this doesn't work):
var url = new window.location("http://www.example.com/some/path?name=value#anchor");
var protocol = url.protocol;
var hash = url.hash;
// etc etc
Is anything like this possible or would I essentially have to create this object myself?

Well, you could use an anchor element to extract the url parts, for example:
var url = document.createElement('a');
url.href = "http://www.example.com/some/path?name=value#anchor";
var protocol = url.protocol;
var hash = url.hash;
alert('protocol: ' + protocol);
alert('hash: ' + hash);
​
It works on all modern browsers and even on IE 5.5+.
Check an example here.

How about use the standard URL object?
const url = new URL("http://www.example.com/some/path?name=value#anchor");
const { hash } = url;
Then console.log(hash) will output #anchor.
Warning: This interface is a bit new, so, if you're not using a transpiler, please, check the compatibility table and do your tests at target browsers.

You can leverage the power of an anchor element
var aLink = document.createElement("a");
aLink.href="http://www.example.com/foo/bar.html?q=123#asdf";
alert(aLink.pathname);

You can parse it in a regex to get the parts as matches... I don't have the full code right now, but this can be used to get the querydata:
var myUrl = window.location.href;
var matches = myUrl.match(/([^\?]+)\?(.+)/);
var queryData = matches[2];
matches[0] is the full string, matches(1) is the first part of the URL (up to the ?)... you could build up a regular expression to parse each part of a string url if you want...
You can also use one of the many libraries already out there for this.