Replacing query string parameter values.

index.js

// Update the appropriate href query string parameter
function paramReplace(name, string, value) {
  // Find the param with regex
  // Grab the first character in the returned string (should be ? or &)
  // Replace our href string with our new value, passing on the name and delimeter
  var re = new RegExp("[\\?&]" + name + "=([^&#]*)"),
      delimeter = re.exec(string)[0].charAt(0),
      newString = string.replace(re, delimeter + name + "=" + value);

  return newString;
}

I think this is better

function queryStringUrlReplacement(url, param, value) 
{
    var re = new RegExp("[\\?&]" + param + "=([^&#]*)"), match = re.exec(url), delimiter, newString;

    if (match === null) {
        // append new param
        var hasQuestionMark = /\?/.test(url); 
        delimiter = hasQuestionMark ? "&" : "?";
        newString = url + delimiter + param + "=" + value;
    } else {
        delimiter = match[0].charAt(0);
        newString = url.replace(re, delimiter + param + "=" + value);
    }

    return newString;
}

This function will add new parameter if not exist before, and will replace the old one if exist, without messing with any of existing querystring parameters.

to use var newUrl = queryStringUrlReplacement('http://www.tomatmerah.com/', 'page', '18');

@slaveofcode Nice work. You might want to update to do a case-insensitive match, otherwise it will duplicate the parameters to the resulting string. Minor update, but overall a great solution.

var re = new RegExp("[\\?&]" + param + "=([^&#]*)", "i"), match = re.exec(url), delimiter, newString;

Using this thread I have compiled a String prototype to easily replace params in a URL enjoy.

// Replace or add parameters to a url
// Author: James Bernard
// email: [email protected]
// Version: 0.5
String.prototype.replaceParam = function(paramsObject, add) 
{
    var originalUrl = this.toString();
    var params = Object.keys(paramsObject);
    var newUrl = originalUrl;
    params.forEach(function(param){
        // Author: iratherscribble@gitHub
        var re = new RegExp("[\\?&]" + param + "=([^&#]*)", "i"), match = re.exec(newUrl), delimiter, newString;
        // =============
        // Author: slaveofcode@gitHub
        if (match === null && add) {
            // append new param
            var hasQuestionMark = /\?/.test(url); 
            delimiter = hasQuestionMark ? "&" : "?";
            newUrl = newUrl + delimiter + param + "=" + paramsObject[param];
        } else if(match){
            delimiter = match[0].charAt(0);
            newUrl = newUrl.replace(re, delimiter + param + "=" + paramsObject[param]);
        } else {
            console.error("Parameter", "'" + param + "'", "Does not exist in url: ", originalUrl); 
            console.error("To add these parameters to this url please change your method call to: replaceParam([Object], [Boolean=true])")
        }
    })

    return newUrl;
}

Patched this to work with urls that contain ?: or &: in their parameters.

// Replace or add parameters to a url
// Author: James Bernard
// email: [email protected]
// Version: 0.6
String.prototype.replaceParam = function(paramsObject, add) 
{
    var originalUrl = this.toString();
    var params = Object.keys(paramsObject);
    var newUrl = originalUrl;
    params.forEach(function(param){
        // Author: iratherscribble@gitHub
        var re = new RegExp("[\\?&:]" + param + "=([^&#]*)", "i"), match = re.exec(newUrl), delimiter, newString;
        // =============
        // Author: slaveofcode@gitHub
        if (match === null && add) {
            // append new param
            var hasQuestionMark = /\?/.test(url); 
            var hasColon = /\:/.test(url);
            delimiter = hasColon ? (hasQuestionMark ? "&:" : "?:") : (hasQuestionMark ? "&" : "?");
            newUrl = newUrl + delimiter + param + "=" + paramsObject[param];
        } else if(match){
            delimiter = match[0].charAt(0);
            newUrl = newUrl.replace(re, delimiter + param + "=" + paramsObject[param]);
        } else {
            console.error("Parameter", "'" + param + "'", "Does not exist in url: ", originalUrl); 
            console.error("To add these parameters to this url please change your method call to: replaceParam([Object], [Boolean=true])")
        }
    })

    return newUrl;
}

@jbernard1: Thanks for the code! Noticed that these two lines:

            var hasQuestionMark = /\?/.test(url); 
            var hasColon = /\:/.test(url);

Should be:

            var hasQuestionMark = /\?/.test(newUrl); 
            var hasColon = /\:/.test(newUrl);

Cheers! :)

This is my preference, and it covers the cases I can think of. Can anyone think of a way to reduce it to a single replace?

function setParam(uri, key, val) {
    return uri
        .replace(new RegExp("([?&]"+key+"(?=[=&#]|$)[^#&]*|(?=#|$))"), "&"+key+"="+encodeURIComponent(val))
        .replace(/^([^?&]+)&/, "$1?");
}

/**

• 替换url参数
• @param {String} name 参数名
• @param {String} value 参数值
• @param {String} url 如果该值存在,则以该值为基准替换
  /
  function replaceUrlParam(name, value, newUrl) {
  let urlMark = '';
  let url = newUrl || location.href;
  let nameIndex = url.indexOf(name);
  //删除参数
  if (value === '') {
  //取当前参数前一位字符
  urlMark = url.charAt(nameIndex - 1);
  if (!/?|&/.test(urlMark)) {
  urlMark = '';
  }
  let reg = new RegExp("\" + urlMark + name + '=' + "[^&]");
  url = url.replace(reg, '');
  }
  //如果一个参数都没有
  else if (window.location.search === "" && new URL(location.href).searchParams.get(url) === '') {
  urlMark = '?';
  url = url + urlMark + name + '=' + value;
  }
  //有参数, 有当前参数
  else if (nameIndex > -1) {
  //这个urlMark 可能会是 ? 或 &
  urlMark = url.charAt(nameIndex - 1);
  let reg = new RegExp("\" + urlMark + name + '=' + "[^&]*");
  url = url.replace(reg, urlMark + name + '=' + value);
  }
  //有参数，但没有当前参数
  else if (nameIndex === -1) {
  urlMark = '&';
  url = url + urlMark + name + '=' + value;
  }
  //替换为正确的符号参数
  if (url.indexOf('?') === -1) {
  let matchParam = url.match('&');
  if (matchParam !== null) {
  url = url.replace(/&/, '?');
  }
  }
  return url;
  }

this is better

To replace all the query parameters with given value you can use something like this:

url.replace(/([?&])(((?![?&#=]).)*=)((?![?&#=]).)*/g, '$1$2xxx');