const touchCache should be var or let, not const

[gayeagle]

MDN URL

https://developer.mozilla.org/en-US/docs/Web/API/Touch_events/Multi-touch_interaction

What specific section or headline is this issue about?

Section "Global State"

What information was incorrect, unhelpful, or incomplete?

The included JS sample appears as such:

const logEvents = false;

// Touch Point cache
const tpCache = [];

which conflicts with the code example as written for the Move/Pinch/Zoom handler see

  if (ev.targetTouches.length === 2 && ev.changedTouches.length === 2) {
    // Check if the two target touches are the same ones that started
    // the 2-touch
    const point1 = tpCache.findLastIndex(
      (tp) => tp.identifier === ev.targetTouches[0].identifier,
    );
    const point2 = tpCache.findLastIndex(
      (tp) => tp.identifier === ev.targetTouches[1].identifier,
    );

    if (point1 >= 0 && point2 >= 0) {
      // ... omitted for brevity ...
    } else {
      // empty tpCache
      tpCache = []; // <--- issue here
    }

What did you expect to see?

The issue is pretty simple, during some quality update to the demos and tutorials, someone updated the variable declaration from var to const without realizing that the reassignment to an empty array is not permitted.

Do you have any supporting links, references, or citations?

No response

Do you have anything more you want to share?

No response

MDN metadata

Page report details

• Folder: en-us/web/api/touch_events/multi-touch_interaction
• MDN URL: https://developer.mozilla.org/en-US/docs/Web/API/Touch_events/Multi-touch_interaction
• GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/web/api/touch_events/multi-touch_interaction/index.md
• Last commit: acfe8c9
• Document last modified: 2023-07-07T07:19:19.000Z

[minimalsm]

Hey @gayeagle, nice catch 💪!

I think it would be better to clear the array without reassignment. That way, we prevent bugs where it might accidentally be reassigned elsewhere.

e.g.

  function clearTouchCache() {
    tpCache.length = 0
  }

  ...

  if (point1 >= 0 && point2 >= 0) {
    // ... 
  } else {
    clearTouchCache()
  }

Happy to open a PR if you don't want to :)