此代码中async的含义[关闭]

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var response = $.ajax({
            url: "/Master/chkDuptindustryid",
            type: "POST",
            data: "{ 'systemid':'" + systemid + "'}",
            async: false,
            contentType: "application/json; charset=utf-8",
            success: function (response) {

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Answer 1

What is says: you can do a synchronous call instead of asynchronous one, which is a default.

http://api.jquery.com/jquery.ajax/

By default, all requests are sent asynchronously (i.e. this is set to true by default). If you need synchronous requests, set this option to false. Cross-domain requests and dataType: "jsonp" requests do not support synchronous operation. Note that synchronous requests may temporarily lock the browser, disabling any actions while the request is active. As of jQuery 1.8, the use of async: false with jqXHR ($.Deferred) is deprecated; you must use the success/error/complete callback options instead of the corresponding methods of the jqXHR object such as jqXHR.done() or the deprecated jqXHR.success().