Function returning undefined in Geocoder

Question

I am using Google maps v3 geocoder to geocode an address then pass the 2 coordinate points from the jQuery file to a PHP file using getJSON.

Problem: However, I notice that the function that does the geocoding function keeps returning an undefined value! Thus the PHP file receives a undefined variable. Where did I go wrong?

jQuery Code

var search_latlng = geocodeAddress(search_location);
console.log(search_latlng);

$.getJSON('/main/get_places', {search_location: search_latlng}, function(json){
        $("#result_listing").html('');
 .
 .
 .

Geocoder JS function

function geocodeAddress(address) {

    var latlng = new Array(2);

    geocoder.geocode( { 'address': address}, function(results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
            latlng[0] = results[0].geometry.location.lat();
            latlng[1] = results[0].geometry.location.lng();
            return latlng;
        } else {
            console.log("Geocode was not successful for the following reason: " + status);
        }
    });
}

Pointy · Accepted Answer · 2011-11-02 12:23:40Z

4

You can't return a value from that function via the callback to the Google code. It makes no sense; the "geocode()" function is asynchronous. The outer function will have returned by the time that your callback runs.

The proper way to do this is to mimic the Google API itself: give your function a callback parameter, and perform your "afterwards" work from there:

function geocodeAddress(address, callback) {

    var latlng = new Array(2);

    geocoder.geocode( { 'address': address}, function(results, status) {
        if (status == google.maps.GeocoderStatus.OK) {
            latlng[0] = results[0].geometry.location.lat();
            latlng[1] = results[0].geometry.location.lng();
            callback(latlng); // call the callback function here
        } else {
            console.log("Geocode was not successful for the following reason: " + status);
        }
    });
}

edit — as an example of how you'd use this:

geocodeAddress(search_location, function(search_latlng) {
  console.log(search_latlng);
  $.getJSON('/main/get_places', {search_location: search_latlng}, function(json){
    $("#result_listing").html('');
    // ...
  });
});

It's like your original code, but instead of having the geocode result returned to your code, it's passed as the parameter to the callback function you provide.

edited Nov 2, 2011 at 12:23

answered Nov 1, 2011 at 13:56

Pointy

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4 Comments

Nyxynyx Over a year ago

Thanks for the reply! So callback is an ordinary function defined elsewhere that I pass into geocoderAddress()? Can the callback() function take the latlng variable and return it to another variable search_latlng to pass to the getJSON function?

Pointy Over a year ago

What you're doing, essentially, is exactly the same thing that the Google API does to handle the core asynchronous transaction (the underlying HTTP request that satisfies the geocoding query). You pass a function to the Google API, so in turn your API is written so that when you call it from elsewhere, you pass in a handler function.

Nyxynyx Over a year ago

Hi Pointy, my javascript isnt very good, so I can' understand you. Can you write an example callback function code in the code you posted? I tried googling for it but doesnt seem to be the callback function that I understand you are telling me about.

Pointy Over a year ago

Well OK, but of course I have no idea what you want to do with the lat/lng information ...

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