为什么我的clearInterval不起作用？

Question

Using the node.js,I set a timer to connect the TCP server.when it success ,it will be cleared.However it doesn't work.just like this:

var net = require('net');
var connectTransferTick=null;

var client ;
client = new net.Socket();
function clientConnect() {
    client.connect(8009, '127.0.0.1', function () {
        console.log('success，clear timer');
        if(connectTransferTick!=null);
        {
            clearInterval(connectTransferTick);
        }
    });
    client.on('error',function()
    {});
    client.on('close', function () {
        console.log('The server had been closed,Try to connect it again later');
        if(connectTransferTick!=null)
        {
            console.log(clearInterval(connectTransferTick));
        }
        connectTransferTick = setInterval(clientConnect,1000);
    });
}
clientConnect();

Run it ,you will find the timer cann't clear.

while,I Just put this code in the function clientConnect(),like this:

function clientConnect() {
    client = new net.Socket();

The timer could be cleared.I can't explaint it.why ? please help me.Thanks a lot.

Answer 1

I think because setInterval is called when the Socket connection is closed, but you're attempting to cancel the interval earlier than this, when the Socket is first opened.

Thus, when you call

clearInterval(connectTransferTick)

at this point connectTransferTick is still null , because

connectTransferTick = setInterval()

has not yet happened.

Answer 2

Because when the close is met, it will cause the clientConnect to be call at least again, and register another onclose to client. So every time the close is met, you register more setInterval while you can only clear the latest.

So

function clientConnect() {
    client = new net.Socket();

works because you create a new socket, and it haven't defined the onclose handler yet, so it won't execute setInterval more than once.

So you should use a flag to prevent register the events many times:

var net = require('net');
var connectTransferTick=null;

var client ;
client = new net.Socket();
function clientConnect(isInited) {
    client.connect(8009, '127.0.0.1', function () {
        console.log('success，clear timer');
        if(connectTransferTick!=null);
        {
            clearInterval(connectTransferTick);
        }
    });

    // Prevent events registered many times.
    if (!isInited) {
        client.on('error',function(){});
        client.on('close', function () {
            console.log('The server had been closed,Try to connect it again later');
            if(connectTransferTick!=null)
            {
                console.log(clearInterval(connectTransferTick));
            }
            // Pass a flag to the clientConnect
            connectTransferTick = setInterval(clientConnect,1000, true);
        });    
    }

}
clientConnect();

In addition, I think setTimeout should be enough to handle this?

var net = require('net');

var client ;
client = new net.Socket();
function clientConnect(isInited) {
    client.connect(8009, '127.0.0.1', function () {
        console.log('success，clear timer');
    });

    // Prevent events registered many times.
    if (!isInited) {
        client.on('error',function(){});
        client.on('close', function () {
            console.log('The server had been closed,Try to connect it again later');
            connectTransferTick = setTimeout(clientConnect,1000, true);
        });    
    }

}
clientConnect();

Answer 3

Some information/advice on the use of interval identifiers:

Node.js:

The return value of setInterval() is an object, which contains all of the information about the interval you created. Even after calling clearInterval() with the object as an parameter, the object is not set to null. You should check the object's _repeat flag to check whether the interval is running or not.

var interval_id = setInterval(function() {  }, 10000);

if (interval_id._repeat)
{
    clearInterval(interval_id);
}

Client-side javascript:

The return value of setInterval() is an int, which is the id of the interval you created. When you call clearInterval() , it doesn't unset the variable that stores this integer id. You should do this manually after calling clearInterval() if you are going to use it as a flag for whether the interval is running or not.

var interval_id = setInterval(function() {  }, 10000);

if (interval_id)
{
    clearInterval(interval_id);
    interval_id = null;
}