jquery ajax调用success，如何在包装器javascript函数中更改全局变量?

function ajax_test(str1){ 
  var url = "None" 
  jq.ajax({
    type:'post', 
    cache: false, 
    url: 'https://....' + str1, 
    success: function(data, status, xhr){ 
      url=data; 
    }, 
    error: function (xhr, status, e) {  
    }, 
    async: true, 
    dataType: 'json' 
  }); 
  return url 
} 
function ajax_test(str1){ 
  var url = "None"