jquery ajax Function undefined

Question

Returning a response from a function every time end up as undefined function!!

var result = Checkusers();(result is undefined) 

function CheckUser() {

    var EmpName = $("#txtName").val();

    $.ajax({        
        type: "POST",
        url: location.pathname + "/UserExist",
        data: "{Name:'" + EmpName + "'}",
        contentType: "application/json; charset=utf-8",
        datatype: "jsondata",
        async: "true",
        success: function (response) {
            console.log(response.d);
            var obj = eval('(' + response.d + ')');
            return obj;
        },
        error: function (response) {
            alert(response.status + ' ' + response.statusText);         
        }
    });
}

i am calling this function as

var Result = CheckUser();
if(Result== false){ 
    //do something
} else{
    //do something
}

I have struggling with this from past one day!! I read in a section that it is because of 'Ajax is Asynchronous' . But how could i handle it??

are you sure your response is an object? what is the output of console? — Mostafa Talebi
– Mostafa Talebi, Commented Mar 25, 2014 at 7:42

Szilard Muzsi · Accepted Answer · 2014-03-25 07:50:37Z

1

You're better off passing a callback function to the CheckUser

function CheckUser(callback) {

    var EmpName = $("#txtName").val();

    $.ajax({        
        type: "POST",
        url: location.pathname + "/UserExist",
        data: "{Name:'" + EmpName + "'}",
        contentType: "application/json; charset=utf-8",
        datatype: "jsondata",
        async: "true",
        success: function (response) {
            console.log(response.d);
            var obj = eval('(' + response.d + ')');
            callback(obj);
        },
        error: function (response) {
            alert(response.status + ' ' + response.statusText);
            callback(null);         
        }
    });
}

You would then call this function as so

CheckUser(function (res) {
    if (res === null) {
       //false
    } else {
       //true
    }
});

answered Mar 25, 2014 at 7:50

Szilard Muzsi

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Comments

Joakim M · Accepted Answer · 2014-03-25 07:42:08Z

0

Typo

Checkusers -with s

CheckUser() -without s

answered Mar 25, 2014 at 7:42

Joakim M

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2 Comments

user3452210 Over a year ago

come on it was mistake in question posting!! In real code both are same!!

Joakim M Over a year ago

No worries. I ain't downvoting or nothing. Everyone can make a mistake :)

Anoop Joshi P · Accepted Answer · 2014-03-25 07:47:59Z

change

datatype:'jsondata'

to

 dataType: "json"

Since the ajax is asynchronous you cant return data like that. You need to write the things on success handler of ajax

$.ajax({
type: "POST",
url: location.pathname + "/UserExist",
data: "{Name:'" + EmpName + "'}",
contentType: "application/json; charset=utf-8",
dataType: "json",
async: "true",
success: function (response) {
   //do your stuff here

},
error: function (response) {
    alert(response.status + ' ' + response.statusText);
}
});

If you want to return data from ajax, you should use async : false for that

function CheckUser() {
var EmpName = $("#txtName").val();
var CheckUser;
$.ajax({
    type: "POST",
    url: location.pathname + "/UserExist",
    data: "{Name:'" + EmpName + "'}",
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    async: false,
    // ...
    success: function (jsonData) {
        CheckUser = jsonData
    }
});
return CheckUser
}

but its not a good approach, it will freeze the browser

s4m0k · Accepted Answer · 2014-03-25 08:00:51Z

function CheckUser() doesn't have any return statement that is why your result is always undefined.

Pass a callback instead to your function and invoke it upon success or error of your ajax call.

something like this :

function CheckUser(callback) {

var EmpName = $("#txtName").val();

$.ajax({        
    type: "POST",
    url: location.pathname + "/UserExist",
    data: "{Name:'" + EmpName + "'}",
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    async: "true",
    success: function (response) {
        console.log(response.d);
        var obj = eval('(' + response.d + ')');
        callback(null, obj);
    },
    error: function (response) {
        alert(response.status + ' ' + response.statusText);
        callback(response);         
    }
});
}

then :

var Result = CheckUser(function ( err, data) {
    // check if no err then process whatever data format you have
});

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