从函数返回，ajax [重复]

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                        <a href="/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call" dir="ltr">How do I return the response from an asynchronous call?</a>
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            <div class="grid--cell mb0 mt8">Closed <span title="2015-06-18 12:25:52Z" class="relativetime">4 years ago</span>.</div>
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Ajax get data normal, but i dont know how return varname from if statement, with inside loop, with inside function ;). How can return var username from this statement? Thanks.

    $.ajax({
         dataType: 'json',
         url: 'example.com',
         type: 'POST',
         success: function (data) {
           for (var i = 0; i < data.users.length; i++) {
             if (user_id == data.users[i].id) {

                var username = data.users[i].username;
                return username; // !!!How can return this

                    };
                };
            }
        })

console.log(username) // error: username is not defined

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Answer 1

By default, ajax will be executed asynchronously. This means that the result returned has to be handled in the callback:

$.ajax({
  dataType: 'json',
  url: 'example.com',
  type: 'POST',
  success: function (data) {
    for (var i = 0; i < data.users.length; i++) {
      if (user_id == data.users[i].id) {
        var username = data.users[i].username;
        console.log(username);
      }
    }
  }
});

ajax could be executed with the async set to false but this is usually not recommended as it will lock the UI until you get the response from the server.