Return Single Value From Google Fusion Table

Question

I am trying to retrieve a single value from a Google Fusion table but am having problems doing so due to the asynchronous nature of the call. Any ideas how to do this? Here is what I have tried so far:

function getVal() {
    var queryText = encodeURIComponent(query);

    var gvizQuery = new google.visualization.Query(
        'http://www.google.com/fusiontables/gvizdata?tq=' + queryText);

        gvizQuery.send(function (response) {
                var dt = response.getDataTable()
                alert(dt.getValue(0, 0)); // Works, returns a value

                return dt.getValue(0, 0);
    });

var value = getVal(); // Undefined

Answer 1

I will answer to the question that you have asked in the comments as that is more clear and I guess that's the problem you are looking to solve.

Use a Javascript Promise to handle such Async calls. (An overview of JS promise).

A promise will help you to wait for the response and then do operation on the same.

One example-

if (window.Promise) {
  console.log('Promise found');

  var promise = new Promise(function(resolve, reject) {
    var request = new XMLHttpRequest();

    request.open('GET', 'http://api.icndb.com/jokes/random');
    request.onload = function() {
      if (request.status == 200) {
        resolve(request.response); // we got data here, so resolve the Promise
      } else {
        reject(Error(request.statusText)); // status is not 200 OK, so reject
      }
    };

    request.onerror = function() {
      reject(Error('Error fetching data.')); // error occurred, reject the  Promise
    };

    request.send(); //send the request
  });

  console.log('Asynchronous request made.');

  promise.then(function(data) {
    console.log('Got data! Promise fulfilled.');
    document.getElementsByTagName('body')[0].textContent = JSON.parse(data).value.joke;
  }, function(error) {
    console.log('Promise rejected.');
    console.log(error.message);
  });
} else {
  console.log('Promise not available');
}

Your example should looks something similar to this-

function getVal() {
  var promise = new Promise(function(resolve, reject) {
    var queryText = encodeURIComponent(query);

    var gvizQuery = new google.visualization.Query(
        'http://www.google.com/fusiontables/gvizdata?tq=' + queryText);

        gvizQuery.send(function (response) {
                var dt = response.getDataTable()

                resolve(dt.getValue(0, 0));
    });
  reject(false);
  }
}
var value = getVal();

Please read on Javascript Promises, it will help you a lot.