[🐛 Bug]: isExisting calls findElements (multiple), a potentially expensive op

WebdriverIO Version

latest

Node.js Version

14

Mode

WDIO Testrunner

Which capabilities are you using?

{
  platformName: "iOS"
}

What happened?

Like the title says, under the hood, webdriverIO calls findElements (multiple) when using isExisting and waitForExist. https://github.com/webdriverio/webdriverio/blob/f1313735cd3441dc172d3955479575854e64a306/packages/webdriverio/src/commands/element/isExisting.ts#L58

Only findElement (single) calls should be needed to assert whether or not the element / selector exists.

This becomes a problem because findElements calls can be quite expensive. An example would be large scrollable lists on iOS apps, they can take 30+ seconds.

What is your expected behavior?

No call to findElements should be made on isExisting as it is not needed and in fact can needlessly hang the command.

How to reproduce the bug.

Context: I'm testing a mobile app with Appium, testing a scrollable list. Scrollable lists on iOS always possess all the list items, unlike Android which loads the list items into view as you scroll/swipe up and down. Therefore finding multiple elements on iOS can lead to a time consuming operation for large lists. In the same situation however, single findElement call is cheap and fast. Assume a findElements call takes 30+ seconds to resolve and we are trying to purposely avoid it

The flow goes something like this:

1. Wait for the (scrollable) list container
2. Then wait for the list items to load within the scrollable list
3. Irrelevant, do whatever else, expectation, whatever

This translates to some code resembling this:

get list() {
  return $('id=list');
}

get items() {
  return $$('id=list-item');
}

waitForItems = (title) => {
  // We previously already waited for the list container
  // We want to wait for the list items to load within the scrollable list
  // Assume they appear instantly

  // Option 1, takes 30+ seconds because of findElements call
  browser.waitUntil(() => this.items.length);

  // Option 2, takes 30+ seconds because of findElements call
  browser.waitUntil(() => $('id=list-item').isExisting());

  // Option 3, takes 30+ seconds because of findElements call
  $('id=list-item').waitForExist();

  // Workaround to save time
  // Option 4, findElements not called, findElement called, 2 seconds
  browser.waitUntil(() => !!$('id=list-item').elementId);
}

Relevant log output

No relevant logs.

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