Here is modified stenix's code, it's not perfect but it handles cases where there is a param in url that contains provided parameter, like:
/search?searchquery=text and 'query' is provided.
In this case searchquery param value is changed.
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
}