javascript javascript返回值总是未定义
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javascript return value is always undefined
提问by Mustafa ELnagar
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 !!
我正在尝试检索分离函数的 2 个属性，并在函数结束之前调试这些值，它们有一个值，但返回值始终未定义，我不知道为什么！！
the .js file
.js 文件
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
我收到了 lan 和 lat 值的警报
but when I call on separated file it return undefined return value
但是当我调用分离的文件时，它返回未定义的返回值
<!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>
回答by iurisilvio
You are returning in the anonymous function and this value is never assigned to anything. You can do what you want with a callback.
您正在匿名函数中返回，并且这个值永远不会分配给任何东西。你可以用回调做你想做的事。
// 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...
而你的测试功能...
function test(){
var out;
STAAPlanlat(function(lat, lon) { out = lat; });
}
回答by jeschafe
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:
因为您不是从主函数返回它，而是从嵌入的匿名函数返回它，该函数对它没有做任何事情。做这个：
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");
}
回答by jagm
because function STAAPlanlat doesn't return any value. your anonymous function returns lanbut it is asynchronous callback.
add this before return lan;:
因为函数 STAAPlanlat 不返回任何值。您的匿名函数返回lan但它是异步回调。在此之前添加return lan;：
document.getElementById("STAAPlanlat").value = "lan is" + lan;
