javascript return value is always undefined
Question
I'm trying to retrieve the 2 attributes of seprated function and I debug there values before the end of the function and they have a value but the return value is alwas undifined I don't know why !!
the .js file
function STAAPlanlat(){
alert ("the function");
if (navigator.geolocation) {
//we supposed to call the handlers of the expections
navigator.geolocation.watchPosition(function(position) {
alert("show position ");
// x.innerHTML="Latitude: " + position.coords.latitude +"<br />Longitude: " + position.coords.longitude;
var lat=position.coords.latitude;
var lan=position.coords.longitude;
//x.innnerHTML=out
alert(lat+"<"+lan);
return lan;
});
} else {
alert("error");
}
}
I got the alert with the values of the lan and lat
but when I call on separated file it return undefined return value
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="STAAP1.2.js"> </script>
<script type="text/javascript">
function test(){
var out=STAAPlanlat();
document.getElementById("STAAPlanlat").value = "lan is"+out;
//document.writeln("lan is"+out);
}
</script>
</head>
<body>
<p id="STAAPlanlat">Test the division</p>
<button onclick="test()">STAAPlanlat()</button>
<button onClick="alertme()" >Alert</button>
</body>
</html>
3 answers
solution1
3 2012-07-11 21:36:41
You are returning in the anonymous function and this value is never assigned to anything. You can do what you want with a callback.
// untested code, hope it works
function STAAPlanlat(callback){
alert ("the function");
if (navigator.geolocation) {
navigator.geolocation.watchPosition(function(position) {
var lat=position.coords.latitude;
var lan=position.coords.longitude;
callback(lat, lan);
});
}
else{
alert("error");
}
}
And your test function...
function test(){
var out;
STAAPlanlat(function(lat, lon) { out = lat; });
}
solution2
2 2012-07-11 21:33:27
Cause you're not returning it from the main function, you're returning it from the embedded anonymous function which isn't doing anything with it. Do this:
function STAAPlanlat(){
var lat;
var lan;
alert ("the function");
if (navigator.geolocation) {
//we supposed to call the handlers of the expections
navigator.geolocation.watchPosition(function(position) {
alert("show position ");
// x.innerHTML="Latitude: " + position.coords.latitude +"<br />Longitude: " + position.coords.longitude;
lat=position.coords.latitude;
lan=position.coords.longitude;
//x.innnerHTML=out
alert(lat+"<"+lan);
});
return lan;
}
else
alert("error");
}
solution3
0 2012-07-11 21:33:51
because function STAAPlanlat doesn't return any value. your anonymous function returns lan but it is asynchronous callback. add this before return lan; :
document.getElementById("STAAPlanlat").value = "lan is" + lan;
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