If Timer.clear is passed a cleared ID

[stc1988]

SyntaxError: C: xsGetHostData: invalid host data (in clear)! occurs with code like the following.

const intervalId = setInterval(() => {
  console.log("Tick");
}, 1000);

setTimeout(() => {
  console.log("clear")
  clearInterval(intervalId)
  clearInterval(intervalId)

}, 5000)

Even with code like the following in a browser or Node.js, no error will occur.

const intervalId = setInterval(() => {
  console.log("Tick");
}, 1000);

setTimeout(() => {
  console.log("clear")
  clearInterval(intervalId)
  clearInterval(intervalId)

}, 5000)

If Timer.clear is passed a value of undefined or null for the ID, no exception is generated.

Timer.clear documentationsays this, but is it necessary to set a cleared ID to null?

[phoddie]

Timer.clear() is not clearInterval(). The documentation accurately describes the behavior. The unit tests confirm the expected error on double close.

Are you suggesting that Timer.clear() adopt the silent failure behavior of clearInterval()? That is convenient for emulation of clearInterval(). It is inconsistent with the general behavior of the Moddable SDK (and ECMAScript) which is to throw an exception on invalid object. There is an exception to this on close() which is generally safe to call multiple time (and clear is analogous to close).

To try that, update the start of xs_timer_clear:

void xs_timer_clear(xsMachine *the)
{
	modTimerScript ts;

	if (0 == xsmcArgc)
		return;

	modTimer timer = xsGetHostDataIf(xsArg(0));
	if ((C_NULL == timer) || (xsGetHostHooksIf(xsArg(0)) != &modTimerHooks))
		return;
	
	ts = (modTimerScript)modTimerGetRefcon(timer);

The unit test at $MODDABLE/tests/modules/base/timer/clear.js needs to be updated in a few places:

/*---
description: 
flags: [async, module]
---*/

import Timer from "timer";

Timer.clear(Timer.set(() => {}, 1));
Timer.clear();	//  "no argument"
Timer.clear(new $TESTMC.HostObject);	// "clear arbitrary host object"

Timer.clear(undefined); 
Timer.clear(null); 

const t = Timer.set(() => {}, 1);
Timer.clear(t);
Timer.clear(t);  // "double clear")

let t1, t2, t3, t4;
t1 = Timer.set(() => {
	Timer.clear(t2);
}, 2);

t2 = Timer.set(() => {
	$DONE("t2 should not be called");
}, 4);

t3 = Timer.set(() => {
	$DONE("t3 should not be called");
}, 3);
Timer.clear(t3);

// crash prior to commit c317ea0
t4 = Timer.set(() => {
	Timer.set(() => {
		try {
			Timer.clear(t4);
		}
		catch (e) {
			$DONE(e);
		}
	}, 1);
}, 1);


Timer.set(() => $DONE(), 8);

[stc1988]

Are you suggesting that Timer.clear() adopt the silent failure behavior of clearInterval()?

I hadn’t thought that far, but I wanted to know the intended behavior of Timer.clear and and now I understand it.
I’m currently developing with mcpack, and I was trying to use setInterval and clearInterval, but it seems I need to be careful with behaviors like this.

[phoddie]

Thank you for the explanation. It wasn't clear to me that the example above was running under the Moddable SDK. It just looks like browser code. ;) I understand now that you are using mcpack.

In the interest of web compatibility I've committed the changes so that Timer.clear() never throws. That will be in our May release.