How to replace url parameter with javascript/jquery?

The following solution combines other answers and handles some special cases:

• The parameter does not exist in the original url
• The parameter is the only parameter
• The parameter is first or last
• The new parameter value is the same as the old
• The url ends with a ? character
• \b ensures another parameter ending with paramName won’t be matched

Solution:

function replaceUrlParam(url, paramName, paramValue)
{
    if (paramValue == null) {
        paramValue="";
    }
    var pattern = new RegExp('\\b('+paramName+'=).*?(&|#|$)');
    if (url.search(pattern)>=0) {
        return url.replace(pattern,'$1' + paramValue + '$2');
    }
    url = url.replace(/[?#]$/,'');
    return url + (url.indexOf('?')>0 ? '&' : '?') + paramName + '=' + paramValue;
}

Known limitations:

• Does not clear a parameter by setting paramValue to null, instead it sets it to empty string. See https://stackoverflow.com/a/25214672 if you want to remove the parameter.