管道值：Ajax + JQuery

Question

I have a function in which I execute an ajax request and wait till I get a response and return a value but the value returned is undefined. What is wrong?

            function GetVMData(url_s){ 
                return $.ajax({ 
                       url: url_s, 
                       crossDomain: true,  
                       dataType: 'jsonp', 
                       error: function(xhr, status, error) {  
                           alert('failed') 
                        }  
                   }).pipe(function(data) { return data[4]; }); 
            } 

If I print the value of data[4] within the ajax callback it prints the right value, therefore i know the request is going through but when I try this:

            var cord;
            cord = GetVMData(url).done(function(cpu_USG) { 
            return cpu_USG;
            }); 
            alert(cord)

the value of cord is wrong.

Answer 1

    var cord;
    cord = GetVMData(url).done(function(cpu_USG) { 
    return cpu_USG;
    }); 
    alert(cord)

This code runs asynchronously. So you need to perform everything in the callback, like:

    GetVMData(url).done(function(cpu_USG) { 
        alert(cpu_USG);
    });