Asked  7 Months ago    Answers:  5   Viewed   28 times

In a web application that makes use of AJAX calls, I need to submit a request but add a parameter to the end of the URL, for example:

Original URL:


Resulting URL:


Looking for a JavaScript function which parses the URL looking at each parameter, then adds the new parameter or updates the value if one already exists.



A basic implementation which you'll need to adapt would look something like this:

function insertParam(key, value) {
    key = encodeURIComponent(key);
    value = encodeURIComponent(value);

    // kvp looks like ['key1=value1', 'key2=value2', ...]
    var kvp ='&');
    let i=0;

    for(; i<kvp.length; i++){
        if (kvp[i].startsWith(key + '=')) {
            let pair = kvp[i].split('=');
            pair[1] = value;
            kvp[i] = pair.join('=');

    if(i >= kvp.length){
        kvp[kvp.length] = [key,value].join('=');

    // can return this or...
    let params = kvp.join('&');

    // reload page with new params = params;

This is approximately twice as fast as a regex or search based solution, but that depends completely on the length of the querystring and the index of any match

the slow regex method I benchmarked against for completions sake (approx +150% slower)

function insertParam2(key,value)
    key = encodeURIComponent(key); value = encodeURIComponent(value);

    var s =;
    var kvp = key+"="+value;

    var r = new RegExp("(&|\?)"+key+"=[^&]*");

    s = s.replace(r,"$1"+kvp);

    if(!RegExp.$1) {s += (s.length>0 ? '&' : '?') + kvp;};

    //again, do what you will here = s;
Tuesday, June 1, 2021
answered 7 Months ago

Try this. Just pass in the param you want to remove from the URL and the original URL value, and the function will strip it out for you.

function removeParam(key, sourceURL) {
    var rtn = sourceURL.split("?")[0],
        params_arr = [],
        queryString = (sourceURL.indexOf("?") !== -1) ? sourceURL.split("?")[1] : "";
    if (queryString !== "") {
        params_arr = queryString.split("&");
        for (var i = params_arr.length - 1; i >= 0; i -= 1) {
            param = params_arr[i].split("=")[0];
            if (param === key) {
                params_arr.splice(i, 1);
        if (params_arr.length) rtn = rtn + "?" + params_arr.join("&");
    return rtn;

To use it, simply do something like this:

var originalURL = "";
var alteredURL = removeParam("color_id", originalURL);

The var alteredURL will be the output you desire.

Hope it helps!

Wednesday, July 28, 2021
answered 5 Months ago

Well, here's one that replaces anything that's not a letter or a number, and makes it all lower case, like your example.

var s = "John Smith's Cool Page";
var filename = s.replace(/[^a-z0-9]/gi, '_').toLowerCase();


The regular expression is /[^a-z0-9]/gi. Well, actually the gi at the end is just a set of options that are used when the expression is used.

  • i means "ignore upper/lower case differences"
  • g means "global", which really means that every match should be replaced, not just the first one.

So what we're looking as is really just [^a-z0-9]. Let's read it step-by-step:

  • The [ and ] define a "character class", which is a list of single-characters. If you'd write [one], then that would match either 'o' or 'n' or 'e'.
  • However, there's a ^ at the start of the list of characters. That means it should match only characters not in the list.
  • Finally, the list of characters is a-z0-9. Read this as "a through z and 0 through 9". It's is a short way of writing abcdefghijklmnopqrstuvwxyz0123456789.

So basically, what the regular expression says is: "Find every letter that is not between 'a' and 'z' or between '0' and '9'".

Sunday, August 8, 2021
answered 4 Months ago

Here's a tag file I use. Save it as /WEB-INF/tags/replaceParam.tag:

<%@ tag pageEncoding="UTF-8" trimDirectiveWhitespaces="true" %>
<%@ taglib uri="" prefix="c" %>
<%@ attribute name="name" required="true" type="java.lang.String" %>
<%@ attribute name="value" required="true" type="java.lang.String" %>

<c:url value="">

      replaces or adds a param to a URL
      if $name in query then replace its value with $value. 
      copies existing 

    <c:forEach items="${paramValues}" var="p">
            <c:when test="${p.key == name}">
                <c:param name="${name}" value="${value}"/>
                <c:forEach items="${p.value}" var="val">
                    <c:param name="${p.key}" value="${val}"/>

    <%-- if $name not in query, then add --%>
    <c:if test="${empty param[name] }">
        <c:param name="${name}" value="${value}"/>


Usage in another page (ex url is /category/9?page=3):

<%@ taglib prefix="my" tagdir="/WEB-INF/tags" %>

<my:replaceParam name='language' value='en' />

output is /category/8?page=3&language=en

Thursday, September 23, 2021
Yu Sasaki
answered 3 Months ago

There you go:

function getURLParam(key,target){
    var values = [];
    if (!target) target = location.href;

    key = key.replace(/[[]/, "\[").replace(/[]]/, "\]");

    var pattern = key + '=([^&#]+)';
    var o_reg = new RegExp(pattern,'ig');
    while (true){
        var matches = o_reg.exec(target);
        if (matches && matches[1]){
        } else {

    if (!values.length){
        return null;   
    } else {
        return values.length == 1 ? values[0] : values;

var str = '[]=hello&name[]=world&var1=stam';

Friday, October 29, 2021
answered 1 Month ago
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