Node Red setInterval causing stale readings on redeploy - setinterval

Question

I'm tinkering around with Node-Red and have made a my first simple custom node which adds to a counter each time an input is received.
The node also contains a call to setInterval which after ever 5 seconds calls node.send() with the counter value in the msg.payload.
module.exports = function(RED) {
function MyNode(config) {
RED.nodes.createNode(this, config);
var node = this;
var count = 0;
this.on('input', function(msg) {
count++;
});
setInterval(function() {
var msg =
{
payload: { countTotal : count }
};
node.send(msg);
return;
}, 5000); // 5 Second Timer
}
RED.nodes.registerType("my-node", MyNode);
}
If I deploy the flow the node is behaving as expected. However if I redeploy the flow I seem to be receiving two calls from the node.send().
One which is the correct value and the other is the last/stale value that was current before the redeploy.
For example:
Deploy and click input 6 times before 5 seconds
05 seconds: countTotal = 6
10 seconds: countTotal = 6
15 seconds: countTotal = 6
Re-deploy and click input 3 times before 5 seconds
05 seconds: countTotal = 3
05 seconds: countTotal = 6 [Old Stale reading]
If I restart node-red then it starts behaving as I'd expect.
My questions
Is this the correct approach to having a timer within a node, if not what should I be doing? If yes, why is the stale data coming through?
Many thanks.
UPDATE
Off the back off the answer from knolleary I've tried the following change
module.exports = function(RED) {
function MyNode(config) {
RED.nodes.createNode(this, config);
var node = this;
var count = 0;
var timer = setInterval(function() {
var msg = { payload: { countTotal : count }};
node.send(msg);
return;
}, 5000); // 5 Second Timer
this.on('input', function(msg) {
count++;
});
this.on('close', function(msg) {
clearTimeout(timer);
});
}
RED.nodes.registerType("my-node", MyNode);
}
...however now when a the flow is re-deployed, it completely stops!!

Answer 1

You are creating a timer each time a node is created, but at no time are you clearing the timer when the node is 'closed'. That is why you are getting multiple timers firing each time you deploy the node.
You need to add a handler for the close event, and tidy up any resources the node is using or has created - such as the timer.
http://nodered.org/docs/creating-nodes/node-js#closing-the-node