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Json Properties: Difference between revisions
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→The /PropertyListener websocket
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=== The /PropertyListener websocket === | === The /PropertyListener websocket === | ||
The property change listener websocket also sends property objects as change events for the subscribed nodes. | The property change listener websocket also sends property objects as change events for the subscribed nodes. The following is a simple HTML page that shows its usage: | ||
<syntaxhighlight lang="javascript"> | |||
<!-- Sample on how to use a websocket PropertyListener. --> | |||
<!-- Extracted from code in Phi. --> | |||
<!-- FlightGear must be started with HTTP server enabled on port 5701. --> | |||
<!DOCTYPE html> | |||
<html> | |||
<body>GMT time in Flightgear: <input type="text" id="myText" value=""> | |||
<p>Click the button to launch the property listener for property /sim/time/gmt.</p> | |||
<button onclick="myFunction()">Launch</button> | |||
<script> | |||
function myFunction() { | |||
var textfield = document.getElementById("myText"); | |||
var ws = new WebSocket('ws://localhost:5701/PropertyListener') | |||
console.log('web socket readyState is ' + ws.readyState) | |||
ws.onopen = function (ev) { | |||
console.log('onopen') | |||
ws.send(JSON.stringify({ | |||
command: 'addListener', | |||
node: 'sim/time/gmt' | |||
})) | |||
} | |||
ws.onmessage = function (ev) { | |||
try { | |||
var data = JSON.parse(ev.data) | |||
textfield.value = data.value | |||
} catch (e) { | |||
console.log('Exception in onmessage:' + e) | |||
} | |||
} | |||
ws.onclose = function (ev) { | |||
var msg = 'Lost connection to FlightGear.' | |||
alert(msg) | |||
} | |||
ws.onerror = function (ev) { | |||
var msg = 'Error communicating with FlightGear.' | |||
alert(msg) | |||
} | |||
} | |||
</script> | |||
</body> | |||
</html> | |||
</syntaxhighlight> | |||
== Pitfalls == | == Pitfalls == | ||