How to Handle an Exception in the Recursive setTimeout Pattern

Question

If ws.send throws an exception for the code below, I want to ensure that I stop recursively sending and that the client thread ends.

function newAlarm(ws)
{
    ws.send(alarm);
}

function loop(f,t)
{
    setTimeout(() => loop(f,t), t);
    f();
}

loop(() => newAlarm(ws),10000);

I understand that to catch the error for ws.send, I do the following: ws.send(alarm, err => {if(!err){...}}) But I can't figure out how to do this for setTimeout.

SilentLupin · Accepted Answer · 2016-09-22 19:21:40Z

2

Try adding a variable to hold your timer, then clearing it when you want it to stop.

function newAlarm(ws)
{
        ws.send(alarm);
}

function loop(f,t)
{
    var timer = setTimeout(() => loop(f,t), t);
    try{
        f();
    }
    catch{
        clearTimeout(timer);
    }
}

loop(() => newAlarm(ws),10000);

edited Sep 22, 2016 at 19:21

answered Sep 22, 2016 at 19:05

SilentLupin

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3 Comments

Baz Over a year ago

But newAlarm is no longer a pure function.

SilentLupin Over a year ago

Can you put a try-catch around f() in your loop and call clearTimeout(timer) in the catch? It worked for a toy example I tried. I updated the code in my answer.

Baz Over a year ago

This works and I prefer it to your first answer, thanks!

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