Uncaught errors in Observable's cell update handling

[mootari]

Describe the bug

Given three cells:

viewof a = html`<input type=range>`

viewof b = html`<input type=range>`

{
  for await(const v of Generators.input(viewof b)) yield [a, v];
}

performing the following steps:

1. move slider a one or more times
2. move slider b once

will trigger the console error:

Uncaught (in promise) ƒ sn(){throw sn}

The number of errors depends on the number of times a did update before updating b.

The error gets thrown here:

[mootari]

Demo: https://observablehq.com/d/06d276b6c217a129

[mbostock]

Thanks for the report. A fix is up at https://github.com/observablehq/runtime/pull/337.