Question

 function get(){
      $.get('/get.php', function(data) {
          alert('one: ' + data)
          return data;
      });
  }

  var test = get();
  alert('two:' + test);

In get.php is:

<?php echo "number"; ?>

why one alert show me
one: number

but two alert show me
two: undefined

How can i get this value outside function?

Answer 1

The $.get call is asynchronous. That means that you pass it a callback (your function(data) { ... }, which gets executed with the result from the call. You can’t return from inside that callback – when it is executed, your outer function (doing the $.get) has already returned. Instead, try something like this:

// callback will be executed with the response from your GET request
function get(callback){
    $.get('/get.php', callback);
}

// Call get with a callback receiving the response
get(function(data) {
    alert('two:' + data);
});

This is a pattern you will have to get used to when writing javascript code.