# "delay" in function
**URL:** https://discourse.nodered.org/t/delay-in-function/65521
**Category:** FAQs
**Created:** [24 July 2022 08:35 UTC](https://discourse.nodered.org/t/delay-in-function/65521 "2022-07-24T08:35:12Z")
**Posts on this page:** 13
**Page:** 1
### Author:  [@mikabytes](https://discourse.nodered.org/u/mikabytes)
#### Post date: [24 July 2022 08:35 UTC](https://discourse.nodered.org/t/delay-in-function/65521/1 "2022-07-24T08:35:12Z")
I've seen several requests for a delay feature in the "function" node. The typical answer is that there is no delay method in JavaScript. Although this is true, you can easily build your own like this:
```auto
const delay = ms => new Promise(res => setTimeout(res, ms))
for (i = 0; i < 12; i++) {
node.send({
payload: `I've waited ${i*75}ms`,
})
await delay(75)
}
```
This enables a more flexible and powerful way of building flows that are dependent on time.
Next example, I turn on 100 spotlights using MQTT, each one being turned on faster than the next, making it feel like it's speeding up.
```auto
for (i = 0; i < 100; i++) {
node.send({
payload: true,
topic: `livingroom/spotlights/${i}/set`
})
await delay(500 - i * 5)
}
```
---
### Author:  [@TotallyInformation](https://discourse.nodered.org/u/TotallyInformation)
#### Post date: [24 July 2022 13:25 UTC](https://discourse.nodered.org/t/delay-in-function/65521/2 "2022-07-24T13:25:20Z")
Thanks for this. Moving to FAQ's to make it easier for people to find.
---
### Author:  [@TotallyInformation](https://discourse.nodered.org/u/TotallyInformation)
#### Post date: [24 July 2022 13:57 UTC](https://discourse.nodered.org/t/delay-in-function/65521/3 "2022-07-24T13:57:24Z")
I should also have said that I don't know that using a promise and await is always a good idea here? I can see why you've done it for the specific case you've used. But in general, using await will block the exit of the function node (I think - not tested) which may cause issues in certain cases.
Generally, I use setTimeout directly but write the timeout reference to a context variable so that it can be cancelled if needed.
---
### Author:  [@dceejay](https://discourse.nodered.org/u/dceejay)
#### Post date: [24 July 2022 15:14 UTC](https://discourse.nodered.org/t/delay-in-function/65521/4 "2022-07-24T15:14:24Z")
if you do use setTimeout (or setInterval) in a function I think we automatically clear them up on close so unless you need to cancel for other reasons no need to save the handle to it.
---
### Author:  [@davidz](https://discourse.nodered.org/u/davidz)
#### Post date: [24 July 2022 15:27 UTC](https://discourse.nodered.org/t/delay-in-function/65521/5 "2022-07-24T15:27:15Z")
Yes we use exactly the same approach. It is very useful to simplify flows for repeated operations that needs a slight delay in each iteration.
---
### Author:  [@mikabytes](https://discourse.nodered.org/u/mikabytes)
#### Post date: [25 July 2022 07:20 UTC](https://discourse.nodered.org/t/delay-in-function/65521/6 "2022-07-25T07:20:36Z")
I believe it's safe. Timeouts/Intervals should be handled automatically (await/async is just syntactic sugar).
Cancelling execution could be achieved like this (written on phone, untested):
```auto
const delay = ms => new Promise(res => context.set("timer", setTimeout(res, ms)))
for (i = 0; i < 12; i++) {
node.send({
payload: `I've waited ${i*75}ms`,
})
await delay(75)
}
```
```auto
const cancel = () => clearTimeout(context.get("timer"))
if (someCondition) {
cancel()
}
```
---
### Author:  [@TotallyInformation](https://discourse.nodered.org/u/TotallyInformation)
#### Post date: [25 July 2022 09:28 UTC](https://discourse.nodered.org/t/delay-in-function/65521/7 "2022-07-25T09:28:19Z")
> [@mikabytes](#):
>
> I believe it's safe. Timeouts/Intervals should be handled automatically (await/async is just syntactic sugar).
As mentioned. I'm sure that the code you posted is OK. It is more that I'm not entirely convinced that it would be safe in a general sense since I'm sure that I read that there is something about `await` being blocking. So if you had a more complex timeout function, the function node wouldn't exit until it completed. If you had a rapid input of msgs to that fn node, that might cause a backlog.
Anyway, not tested but thought it worth mentioning for future reference. The promise and await aren't really necessary.
---
### Author:  [@knolleary](https://discourse.nodered.org/u/knolleary)
#### Post date: [25 July 2022 09:59 UTC](https://discourse.nodered.org/t/delay-in-function/65521/8 "2022-07-25T09:59:27Z")
> [@TotallyInformation](#):
>
> `await` being blocking
`await` does not block the event loop. It is syntactic sugar for Promises that avoids writing code with lots of callbacks/then-blocks.
---
### Author:  [@TotallyInformation](https://discourse.nodered.org/u/TotallyInformation)
#### Post date: [25 July 2022 19:54 UTC](https://discourse.nodered.org/t/delay-in-function/65521/9 "2022-07-25T19:54:19Z")
I don't think I explained it well. I know that it doesn't block the event loop.
I think this explains the possible pitfalls better than I can:
[Understanding async-await in JavaScript | by Gokul N K | Better Programming](https://betterprogramming.pub/understanding-async-await-in-javascript-1d81bb079b2c).
---
### Author:  [@mikabytes](https://discourse.nodered.org/u/mikabytes)
#### Post date: [28 July 2022 14:55 UTC](https://discourse.nodered.org/t/delay-in-function/65521/10 "2022-07-28T14:55:08Z")
Hmm. I went through that article but still struggle to see the potential problem(s).
Nothing is blocking in the sense that the JavaScript engine will stop. I can imagine Node-RED could potentially have an issue though, is that what you meant?
Could you provide an example that demonstrates the potential issue?
If there is a specific problem related to Node-RED, then I would like to file it as a bug. Perhaps I'll even spend some time fixing it.
---
### Author:  [@TotallyInformation](https://discourse.nodered.org/u/TotallyInformation)
#### Post date: [28 July 2022 15:46 UTC](https://discourse.nodered.org/t/delay-in-function/65521/11 "2022-07-28T15:46:08Z")
> [@mikabytes](#):
>
> I can imagine Node-RED could potentially have an issue though, is that what you meant?
Yes. You could potentially get a backlog of requests that haven't completed.
As I said, the example given is fine and won't be a problem, this was more about people making assumptions about await as a general solution in _all_ cases. It seems to me that there are edge cases that need care (as with much of JavaScript!)
> [@mikabytes](#):
>
> If there is a specific problem related to Node-RED, then I would like to file it as a bug
No "bug", it is a "feature" of how promises with await works. Nothing wrong with node-red.
---
### Author:  [@mikabytes](https://discourse.nodered.org/u/mikabytes)
#### Post date: [28 July 2022 18:13 UTC](https://discourse.nodered.org/t/delay-in-function/65521/12 "2022-07-28T18:13:54Z")
Alright. Thanks for clearing that up, I understand your point now.
The same danger is true for callbacks that never return or very long timeouts. There has to be something wrong with the code itself. await/async or promises is just a detail.
I don't recommend always using this await-delay approach. I prefer the delay node where appropriate because my flows become more visually understandable. This trick is for the case where more flexibility is required.
---
### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [26 September 2022 18:14 UTC](https://discourse.nodered.org/t/delay-in-function/65521/13 "2022-09-26T18:14:50Z")
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