设置当前窗口url中param的值

function set_param(param,value){
    var query = location.search.substring(1);
    var p = new RegExp("(^|&"+param+")=[^&]*");
    if(p.test(query)){
        query = query.replace(p,"$1="+value);
        location.search = '?'+query;
    }else{
        if(query == ''){
            location.search = '?'+param+'='+value;
        }else{
            location.search = '?'+query+'&'+param+'='+value;
        }
    }    
}