How to add Web Method as a source to Bootstrap Taginput?

See more:

C#

ASP.NET

PHP

jQuery

bootstrap

, +

$(document).ready(function () {
             $('[id$=tagsinput]').tagsinput({
                 itemValue: 'value',
                 itemText: 'text',
                 typeahead: {
                     source: function (query) {
                         var str;
                         $.ajax({
                             type: "POST",
                             url: "CityNamesData.asmx/GetCities",
                             contentType: "application/json; charset=utf-8",
                             dataType: "json",
                             success: function (data) {
                                 str = data.d;
                             }
                         });
                         var str1 = $.getJSON(str); 
                          return str1;
                         //var str = $.getJSON('assets/cities.json'); //This line is working fine if we want to retrieve data from json file.
                        
                     }
                 }
             });

//Below code shows tags into the asp.net textbox control
             $('[id$=tagsinput]').tagsinput('add', { "value": 1, "text": "Amsterdam" });
             $('[id$=tagsinput]').tagsinput('add', { "value": 4, "text": "Washington" });
             $('[id$=tagsinput]').tagsinput('add', { "value": 7, "text": "Sydney" });
             $('[id$=tagsinput]').tagsinput('add', { "value": 10, "text": "Beijing" });
             $('[id$=tagsinput]').tagsinput('add', { "value": 13, "text": "Cairo" });
         })

I am trying to save data coming from web method into str1 as follows
var str1 = $.getJSON(str);
return str1;
str1 saves data in the same format as it was previously saved in str.
But still when I have tried to return str1, its not showing suggestions into the textbox.
str and str1 are storing json data into the same format.But it is only showing suggestions when I am returning str.
Can anyone please tell me how to return this data coming from WebMethod so that it would show suggestions in textbox.
I dont know whats wrong with str1.