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Is there any way of getting the GET parameters with pure Javascript?

Let's say I have a page called https://randompagename.com, I know I can send GET parameters to this page using this syntax: https://randompagename.com/?parameter1="one"&parameter2="two".
I also know that on a Node.js web app I have an easy way of getting these parameters inside a variable. However, when I'm using pure frontend Javascript without Node.js, I usually solve this problem with something like:
const myURL = decodeURI(window.location.href)
This way, I discover that my page is https://randompagename.com/?parameter1="one"&parameter2="two" and then I can parse it excluding everything after the first = sign and then splitting everything on &. Well, even though this is functional I'm probably missing an easier way of solving this problem. How can I get GET parameters on a page without using any library?

You can use the URL object https://developer.mozilla.org/en-US/docs/Web/API/URL
If the URL of your page is https://example.com/?name=Jonathan%20Smith&age=18 you could parse out the name and age parameters using:
let searchString = (new URL(document.location)).search; //?name=Jonathan%20Smith&age=18
let params = (new URL(document.location)).searchParams;
let name = params.get('name'); // is the string "Jonathan Smith".
let age = parseInt(params.get('age')); // is the number 18

Use URL Parameter to call a line of text using JS?

I'm hoping to call a line of text by using a simple URL parameter. Say I had an ordered list in javascript and on load of url example.com/?i=14 would get the 14th line in my list and place it where desired.
How can I achieve this?

I'm not sure what you mean by "call a line of text," but maybe you could do this:
var url = window.location.href;
var queryPos = url.indexOf('i=');
var param = url.substr(queryPos + 'i='.length);
Now param will contain the value of the parameter and you could use it to fetch whatever.
But since you're trying to access a value from a URL with JavaScript, it might be better to make use of # as explained here: How do I get the value after hash (#) from a URL using jquery (there are non-jquery answers as well)

Hopefully this is what you need.
To place an array element where you need it on document load
<div id="placeHere"></div>
In JS
document.body.onload = function(){
document.getElementById('placeHere').innerHTML = array[14];
}
jQuery
$(document).ready(function(){
$('#placeHere').html(array[14]);
})

JS split OR Logical Operator

User inputs a web address that I want to get only the tail from, as I do know what site he inputs.
So first I want to remove the "main" URL and get what ever is at the end, so my action is:
Original link: http://example.com/something
var n=e.split("http://example.com/");e=n[1];
And I will get "something"
The problem is that site can also be secured, thus having https not http. Therefore the split wont work.
How do I define a split function, that would work like this:
split("http://example.com/ || https://example.com/")
I do not want to split by looking at "//" or anything of that sort, I want an exact address.

If you like it clear and want to avoid regular expressions, try this:
var n=e.split("http://example.com/",2).pop().split("https://example.com/",2).pop();

If you wish to know the host you can do so by using this code instead in JavaScript:
window.location.host
Source Get The Current Domain Name With Javascript (Not the path, etc.)
You can also use window.location.path to get the URL that was requested, combining those you get:
window.location.host + window.location.pathname
For me, this outputs stackoverflow.com/posts/25203020/edit while writing this reply.

var s = "http://example.com/something";
function split (url) {
var r = /([^:]+):\/\/([^\/]+)\/(.*)/gi;
var a = r.exec(url)
return [a[1], a[2], a[3]];
}

Passing 2 URL Parameters?

I need to pass 2 URL parameters in a URL. The URL originates in an email and the user will click the link directing them to my site. The first parameter triggers a script on the page the second parameter is for a module my CMS will render from the parameter.
First Parameter is : message=1 (This parameter triggers the javascript)
The second Parameter is: name={tag_recipientfirstname} (My CMS will render the module)
The script that is called for the first looks like this:
<script type="text/javascript">
var $j = jQuery.noConflict();
$j(document).ready(function() {
var url = window.location.href;
url = url.toLowerCase();
if (url.indexOf('message=1') != -1) {
$j("a.message").colorbox({
open:true
});
}
$j("a.message").colorbox(); //not related to URL parameter
});
</script>
The second parameter is used on the page as:
<div>
<p>{ module_url,name} (again CMS will render this module)</p>
</div>
EDIT
I realize I left a couple things out:
First: How do I pass both parameters so they will both function as listed above?
And the CMS I am using is Business Catalyst.

//split the `location.search` string at the ampersands
var search_arr = window.location.search.replace('?', '').split('&'),
len = search_arr.length,
get_vars = {},
tmp = [];
//iterate through the key/value pairs and add them to the `get_vars` object
for (var i = 0; i < len; i++) {
tmp = search_arr[i].split('=');
get_vars[tmp[0]] = tmp[1];
}
//you can now access your GET variables through the `get_vars` object like: `get_vars.name`
//you can check for the existence of a certain GET variable like this
if (typeof(get_vars['message-1']) != 'undefined') {
$j("a.message").colorbox({
open:true
});
}
Here is a demo:http://jsfiddle.net/aBH8K/1/ (http://jsfiddle.net/aBH8K/1/show/?message-1=3 to see with get var)
Some related documentation:
window.location: https://developer.mozilla.org/en/DOM/window.location

Your question is not so much about generic development, rather a very specific commercial product; I do not know which plan you subscribed (free o pay-for?) with them but in any case it would be best to go through their support (see also my conclusion)
Nevertheless I'll try to put you on the right track.
Your questions
First,
the url in the email
In the email you will have somehow to build a link with the two parameters you want as #Jasper is explaining.
this means something like:
http://yourwebsite.com/destination/path/?message=1&name={tag_recipientfirstname}
Everything after the question mark is a GET query string.
Parameters are separated by the "&" symbol.
I definitely don't know how properly build urls in BC emails, but I feel like it should be an automated somewhere allowing you to specify additional parameters if you need.
the javascript
What you got will still work. It's not very nice, and you can use Jasper's solution or any other such as How can I get query string values in JavaScript?
Nothing to do then unless you want to make it better and more robust.
Business Catalyst (the page)
You usually have ways in a CMS to retrieve get parameters. Often something like
{ GET.param_name }
One step back
I am no expert with BC, but I have the feeling that you are taking a complicate path for something that is probably already baked in.
Again I suggest you go into their support section (though it's rather confusing I must say!) and try to understand what's the best way to achieve your objective. There are always many ways to skin a poor cat.
If you are getting support in your plan, definitely go that way and try to explain what you objectives are rather then how to achieve the technical solution that you think is the good one!

Javascript & HTML Getting the Current URL

Can anyone help me. I don't use Client-side Javascript often with HTML.
I would like to grab the current url (but only a specific directory) and place the results between a link.
So if the url is /fare/pass/index.html
I want the HTML to be pass

This is a quick and dirty way to do that:
//splits the document.location.href property into an array
var loc_array=document.location.href.split('/');
//have firebug? try a console.log(loc_array);
//this selects the next-to-last member of the array.
var directory=loc[loc.length-2]

url = window.location.href // Not particularly necessary, but may help your readability
url.match('/fare/(.*)/index.html')[1] // would return "pass"

There may be an easier answer, but the simplest thing I can think of is just to get the current URL with window.location and use some type of parsing to get which directory you are looking for.
Then, you can dynamically append the HTML to your page.

This may get you started:
var linkElement = document.getElementById("whatever");
linkElement.innerHTML = document.URL.replace(/^(?:https?:\/\/.*?)?\/.*?\/(.*?)\/.*?$/i,"$1");