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How to add parameter in Javascript and remove previous parameter

I had a code that works but the problem is it just append the parameter instead of replacing it with a new parameter, Here is my working code:
jQuery('#input_1_11').change(function(){
var type = jQuery('#input_1_11').val();
if(type=='Inspection'){
window.location.replace(window.location.href + "?Inspection");
}
else if(type=='Installation'){
window.location.replace(window.location.href + "?Installation");
}
else{
window.location.replace(window.location.href + "?Maintenance");
}
});
what currently happening is for example
www.test.com?Inspection
Then if I click again the input11 it goes to the link
www.test.com?Inspection?Maintenance
What I need is to replace each ?parameter every change by user.

use origin:
window.location.origin + "?Maintenance"
instead of
window.location.href + "?Maintenance"

You can do a thing - get the present url and split it into an array with ? as parameter for split. Get the first element of that array. It will be the url without parameters.
jQuery('#input_1_11').change(function(){
var type = jQuery('#input_1_11').val();
var present = window.location.href.split("?");
if(type=='Inspection'){
window.location.replace(present[0] + "?Inspection");
}
else if(type=='Installation'){
window.location.replace(present[0] + "?Installation");
}
else{
window.location.replace(present[0] + "?Maintenance");
}
});

Remove one parameter name and value in url using jquery

Existing Url
http://example.com/home.php?id=1&branch_id=4&course_id=5
New url
http://example.com/home.php?id=1&branch_id=4
removing course_id from existing url
How to remove one parameter value from url.
Tried below code:
function replaceUrlParam(url, paramName, paramValue){
var pattern = new RegExp('(\\?|\\&)('+paramName+'=).*?(&|$)')
var newUrl=url
if(url.search(pattern)>=0){
newUrl = url.replace(pattern,'$1$2' + paramValue + '$3');
}
else{
newUrl = newUrl + (newUrl.indexOf('?')>0 ? '&' : '?') + paramName + '=' + paramValue
}
return newUrl
}
but its not working...

As you said that you want to use variable instead of directly using .replace(/&course_id=\d+/, ''), you can do it like below:-
Example:-
var re = new RegExp("&course_id=\\d+");
var newUrl="http://example.com/home.php?id=1&branch_id=4&course_id=5";
console.log(newUrl.replace(re, ''));
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

You can simply do that by using this code to remove &course_id=5:
var url = "http://example.com/home.php?id=1&branch_id=4&course_id=5";
url.replace(/([&\?]course_id=5*$|course_id=5&|[?&]course_id=5(?=#))/, '');
It will return you: http://example.com/home.php?id=1&branch_id=4

hyperlink alternate text replacement

At the moment i've got this code, which replaces a span class whith a hyperlink. The hyperlink includes a abbreviation and the alternate texxt for the hyperlink includes the same abbreviation. Now what i want to do is, to somehow replace the second abbreviation in the alternate text of the hyperlink. So that there isn't "click here to visit + 'name of'abbreviation" but instead an alias. So if the abbreviaton is ggl, the alias should be google. But the hyperlink shouldn't use this alias. Can sb help me? thx
(function($) {
var number = "1234567";
function linkBuilder(abbreviation) {
return "<a href='https://www.test.com/" + abbreviation + "?sitenumber=" + number + "default'>Click here to visit " + abbreviation + "</a>";
}
function linkBuilder2(abbreviation2) {
return "<a href='https://www.test.com/" + abbreviation2 + "?sitenumber=" + number + "default'>Click here to visit " + abbreviation2 + "</a>";
}
jQuery(document).ready(function() {
var fl = $(".first-link");
if (fl.length > 0) {
fl.html(linkBuilder(fl.data("abbreviation")));
}
var sl = $(".second-link");
if (sl.length > 0) {
sl.html(linkBuilder2(sl.data("abbreviation2")));
}
});
})(jQuery);

Here is a working jsfiddle:
https://jsfiddle.net/e7qdx031/1/
linkBuilder() should be re-usable, as kalsowerus mentioned.
Another thing that should be mentioned is that the following code returns a collection of elements, not just a single element.
var fl = $(".first-link");
...
var sl = $(".second-link");
The code you have provided will not function properly if there are multiple .first-link classes on the page. So instead I would iterate over each element using $.each() and run the linkBuilder() function on them individually.
As for the linkBuilder function I would modify it to accept the element object, then read the properties to retrieve alias and name. Full name is something that you seemed to indicate you need, but was not present in the code.
(function($) {
var number = "123456";
function linkBuilder($obj) {
var abbreviation = $obj.data('abbreviation');
var name = $obj.data('name');
return "<a href='https://www.test.com/" + abbreviation + "?sitenumber=" + number + "default'>Click here to visit " + name + "</a>";
}
jQuery(document).ready(function() {
$('.first-link, .second-link').each(function(index, obj){
$(obj).html(linkBuilder($(obj)));
});
});
})(jQuery);

What you probably want is something like this:
function linkBuilder(abbreviation, alias) {
return "<a href='https://www.test.com/" + abbreviation + "?sitenumber=" + number + "default'>Click here to visit " + alias + "</a>";
}
Just pass the display-name you want for your link as the second argument.

How to add a class for texts between specific characters?

I'm writing my own blog using Blogger. I want to mark some prominent words. For example, when I write *Red* in an editor. It should automatically add a key class and wrap it with the span tag. So, the final result should be as following:
<span class="key">Red</span>
Now, I am trying to write a JQuery script but it still doesn't work properly.
$markText = $('span').filter(function(){
$t = $(this).text();
return $t.charAt(0) === "*" && $t.charAt(4) === "*"}).each(function() {
$s1 = $t.slice(1,4);
$s2 = $t.slice(5);
$(this).replaceWith('<span class="key">' + $s1+ '</span>' + '<span>'+$s2+'</span>');
});
Please see the demo on jsFiddle

Your code can be fixed by what RaymondM has suggested, but you could try something like this as well:
$markText = $('span').each(function (i, e) {
$e = $(e);
while ($(e).text().indexOf('*') != -1) {
$e.html($e.html().replace('*', '<span class="key">').replace('*', '</span>'));
}
});
This makes use of the fact that the replace method only modifies the first occurrence of the target string.
DEMO

The $t in side the each function should be replaced by $(this).text()
$markText = $('span').filter(function(){
$t = $(this).text();
return $t.charAt(0) === "*" && $t.charAt(4) === "*"}).each(function() {
$s1 = $(this).text().slice(1,4);
$s2 = $(this).text().slice(5);
$(this).replaceWith('<span class="key">' + $s1+ '</span>' + '<span>'+$s2+'</span>');
});

add parameter to links on page using jquery

How do I add let's say something like ajax=1 to all links on my page with jquery. I will also need to check if the url has existing parameters. for example http://example.com/index.php?pl=132 will have to become http://example.com/index.php?pl=132&ajax=1
Also, if the link does not have any parameters, for example http://example.com/index.php, it will become http://example.com/index.php?ajax=1 I want to load the jQuery script on document ready so all links are changed on page load.

You could do something like this:
$(function() {
$("a").attr('href', function(i, h) {
return h + (h.indexOf('?') != -1 ? "&ajax=1" : "?ajax=1");
});
});
On document.ready this looks at every <a>, looks at it's href, if it contains ? already it appends &ajax=1 if it doesn't, it appends ?ajax=1.

Like this:
$(function() {
$('a[href]').attr('href', function(index, href) {
var param = "key=value";
if (href.charAt(href.length - 1) === '?') //Very unlikely
return href + param;
else if (href.indexOf('?') > 0)
return href + '&' + param;
else
return href + '?' + param;
});
})

Here is a solution I put together for native Javascript, it supports existing query strings and anchors:
function addToQueryString(url, key, value) {
var query = url.indexOf('?');
var anchor = url.indexOf('#');
if (query == url.length - 1) {
// Strip any ? on the end of the URL
url = url.substring(0, query);
query = -1;
}
return (anchor > 0 ? url.substring(0, anchor) : url)
+ (query > 0 ? "&" + key + "=" + value : "?" + key + "=" + value)
+ (anchor > 0 ? url.substring(anchor) : "");
}
I've posted my existing tests on JSBin: http://jsbin.com/otapem/2/

If you're interested in plugins, there's the jQuery Query String Object. This will allow you simple checking of parameters in the querystring, and if necessary the ability to add more, remove some, or edit others.

Taking what is above, this is the best way to concatenate parameters to links.
Also avoid link with href like href="Javascript:YourFunction();"
$(function(){
var myRandom = getRandom();
$('a[href]').each(function(i){
var currHref = $(this).attr("href");
var isAfunction = currHref.substring(0,10);
if(isAfunction == "javascript"){
$(this).attr("href",currHref);
}else{
if (currHref.charAt(currHref.length - 1) === '?')
$(this).attr("href",currHref);
else if (currHref.indexOf('?') > 0)
$(this).attr("href",currHref+"&rand="+getRandom());
else
$(this).attr("href",currHref+"?rand="+getRandom());
}
});
});
function getRandom(){
var randomnumber = Math.floor(Math.random()*10000);
return randomnumber;
}

a href must be full and corrected URL.
$(function() {
$('a[href]').attr('href', function(index, href) {
var url = new URL(href);
url.searchParams.set('ajax',1);
return url;
});
})
JSFiddle