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POJavascript Callback Within a Callback
 

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  1. POJavascript Callback Within a Callback
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    <p>I am a stuck as to why I never hit the <code>GETNEARCALLBACK</code> function below. The logic goes something like this:</p> <ol> <li>On Page Load I call <code>INITIALIZE</code></li> <li><code>INITIALIZE</code> happily executes and calls <code>GETSTATIONS</code></li> <li><code>GETSTATIONS</code> does an AJAX request using <code>GETNEARESTSTAIONS</code> as the callback function, and the web server responds with the results of a database query in JSON format.</li> <li><code>GETNEARESTSTAIONS</code> takes the results and creates a Google Maps API distance matrix request using <code>GETNEARCALLBACK</code> as the callback function</li> <li>I run my site and use Firebug to determine that I never get to <code>GETNEARCALLBACK</code>. </li> </ol> <p>I think my use of Google Maps API is correct because if I don't call <code>GETNEARESTSTATIONS</code> from within my AJAX request, it executes properly.</p> <p>function INITIALIZE() { GETPOSITION(); DRAWMAP(); GETADDR(); GETSTATIONS(); }</p> <pre><code>var xmlhttp; function GETSTATIONS() { if(window.XMLHttpRequest) { xmlhttp = new XMLHttpRequest(); } else { xmlhttp = new ActiveXObject("Microsoft.XMLHTTP"); } xmlhttp.onreadystatechange = GETNEARESTSTATION(); xmlhttp.open("GET", "final.php", true); xmlhttp.send(); } var STATIONLIST; function GETNEARESTSTATION() { if(xmlhttp.readyState == 4 &amp;&amp; xmlhttp.status == 200) { STATIONLIST = eval("(" + xmlhttp.responseText + ")"); var LAT = parseFloat(document.getElementById("LATITUDE").value); var LON = parseFloat(document.getElementById("LONGITUDE").value); var latlng = new google.maps.LatLng(LAT, LON); var destinationA = STATIONLIST[0].ADDRESS; var service = new google.maps.DistanceMatrixService(); service.getDistanceMatrix({ origins: [latlng], destinations: [destinationA], travelMode: google.maps.TravelMode.DRIVING, unitSystem: google.maps.UnitSystem.IMPERIAL, avoidHighways: false, avoidTolls: false }, GETNEARCALLBACK); } } function GETNEARCALLBACK(response, status) { if(status == google.maps.DistanceMatrixStatus.OK) { var destinations = response.destinationAddresses; var results = response.rows[0].elements; for(var j = 0; j &lt; results.length; j++) { var element = results[j]; document.getElementById("STATIONADDR").innerHTML = parseFloat(element.distance.value) + " " + response.destinationAddresses[j]; } } } </code></pre>
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    1. USxiaoyi
    1. USDaWisePug
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      1. POJavascript Callback Within a Callback
      1. USJake Hertenstein
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    1. COIs there a particular reason you use all caps for function names? It's very unpleasant to read.
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      1. POJavascript Callback Within a Callback
      1. USI Hate Lazy
    2. COconsole.log the `readyState` value and `status` value right before you check them in the `if` statement... what do you get?
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      1. POJavascript Callback Within a Callback
      1. USStuart
 

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