js to modify URL parameters

function changeURLPar(destiny, par, par_value) 
{ 
var pattern = par+'=([^&]*)'; 
var replaceText = par+'='+par_value; 
if (destiny.match(pattern)) 
{ 
var tmp = '/\\'+par+'=[^&]*/'; 
tmp = destiny.replace(eval(tmp), replaceText); 
return (tmp); 
} 
else 
{ 
if (destiny.match('[\?]')) 
{ 
return destiny+'&'+ replaceText; 
} 
else 
{ 
return destiny+'?'+replaceText; 
} 
} 
return destiny+'\n'+par+'\n'+par_value; 
} 

destiny is the target string, such as http://www.csdn.com/?id=3&ttt=3
par is the parameter name, par_value is the value of the parameter to be changed, the call result is as follows:
var url = window.location.href;
changeURLPar(url, 'id', 99); // http://www.csdn.com/?id=99&ttt=3
changeURLPar(url, 'haha', 33); // http://www.csdn. com/?id=99&ttt=3&haha=33