javascript - Why are ajax calls to two page methods being executed synchronously? -

i have 2 script tags on page, each containing document.ready(), , each of them making ajax call page method.

first 1 loads values select list. second 1 loads tree dom.

<script>   $(document).ready(function() {      $.ajax({          url: 'pagemethods.aspx/gettop50',          async: true,          success: function(data) {            //loads values select list           }          //rest of stuff...      });   }) </script>  <script>   $(document).ready(function() {      $.ajax({          url: 'default.aspx/gettree',          async: true,          success: function(data) {          // loads tree dom          }          //rest of stuff...      });   }) </script> 

why gettree page method keep executing after success callback of gettop50? set breakpoint gettree method serverside, , hit after select list loaded.

the client start both ajax calls 1 after other both "in-flight" @ same time. server 1 complete first , depend upon how server configured (will process multiple requests @ once) , depend upon each request doing.

if server handles 1 request @ time or if blocks on shared resource such database, return first request received before returning second request result - though that's option, not guaranteed option. example, if first request pretty takes longer process second , aren't both contending same shared resource, second request might finish first , return results first.

it possible requests return in random order such 1 return first , other return first. said earlier, depends upon how server processes each request , 1 finishes first.

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also, keep in mind client-side js single threaded when sitting @ client-side js breakpoint somewhere, other js cannot run until current js thread of execution has finished. behavior in breakpoints on server-side, depends upon server execution environment , how works during breakpoint.

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if want debug timing-related things, breakpoint not reliable way test things because hitting breakpoint can affect behavior. instead, should use logging accurate timestamps study exact sequence of events.