Break down the differences between async:false and async:true in Ajax requests

Below I will bring you an article detailing the differences between async:false and async:true in Ajax requests. Let me share it with you now and give it as a reference for everyone.

The example is as follows:

function test(){
  var temp="00";
  $.ajax({
    async: false,
    type : "GET",
    url : 'userL_checkPhone.do',
    complete: function(msg){
      alert('complete');
    },
    success : function(data) {
      alert('success');
      temp=data;
      temp="aa";
    }
  });
  alert(temp);
  }

checkPhone() method in UserLAction

  public void checkPhone() throws IOException {
    this.getServletResponse().setContentType("text/html; charset=UTF-8");
    this.getServletResponse().setHeader("Cache-Control", "no-cache");
    PrintWriter out = this.getServletResponse().getWriter();
    out.print("true");

  }

async: false, (default is true);

When async: false is synchronous, the Ajax request in this test() method locks the entire browser,

Only userL_checkPhone Only after the execution of .do is completed, other operations can be performed.

So the execution result is first alert('success'); alert('complete'); alert("aa");

When async: true, the ajax request is asynchronous. But there is a problem: the ajax request in test() and the subsequent operations are executed asynchronously, so when userL_checkPhone.do has not yet been executed, the operations following the ajax request may have been executed,

So the result is alert('success'); alert('complete'); alert("00");

In this way, you will find that alert("success") and alert(temp) are executed almost simultaneously. So temp is the initialized value temp = "00", not temp="aa";

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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