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Fix #118: Improve isVisible for correctness and performance #116

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merged 7 commits into from
Aug 13, 2019
Merged

Fix #118: Improve isVisible for correctness and performance #116

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68ce4cd
Use correct values in isVisible condition
biancadanforth Jul 19, 2019
335657e
#118: Change isVisible to check for clickability to improve performance
biancadanforth Jul 24, 2019
cfd7a50
#118: Fall back to next best sync solution
biancadanforth Aug 3, 2019
c912f13
Fix #118: Incorporate review feedback
biancadanforth Aug 9, 2019
23f86cf
Fix eslint warnings from #51.
biancadanforth Aug 9, 2019
c0a81db
Incorporate more review feedback
biancadanforth Aug 10, 2019
b96c4e3
Revert operator-linebreak eslint rule
biancadanforth Aug 12, 2019
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1 change: 1 addition & 0 deletions .eslintrc.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,7 @@ rules:
no-var: warn
no-warning-comments: [warn, {terms: [xxx, fixme, hack], location: start}]
object-shorthand: [error, properties]
operator-linebreak: [error, after]
prefer-const: off
quotes: [error, single, {avoidEscape: true, allowTemplateLiterals: true}]
semi: [error, always]
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22 changes: 11 additions & 11 deletions utilsForFrontend.mjs
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Expand Up @@ -160,8 +160,8 @@ export function *inlineTexts(element, shouldTraverse = element => true) {
for (let child of walk(element,
element => !(isBlock(element) ||
element.tagName === 'SCRIPT' &&
element.tagName === 'STYLE')
&& shouldTraverse(element))) {
element.tagName === 'STYLE') &&
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I think this actually make it harder to understand. I don't remember writing this (though I probably did), but here's how I read the original:

The ! lines up with the &&, suggesting that 2 clauses are ANDed together. That's what's actually going on.

When you move the 2nd &&, the 2 &&s line up exactly, and it starts looking like shouldTraverse is just one more clause in the earlier &&, unless you take the time to painstakingly balance the parens.

So I think the original indentation visually conveys the structure more clearly. Does that make sense?

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I see what you mean, though that prevents us from having an eslint rule to cover it, as leaving this as-is is not consistent (from eslint's perspective) with changing the other one.

I'm happy to change it back as you prefer, however.

shouldTraverse(element))) {
if (child.nodeType === child.TEXT_NODE) {
// wholeText() is not implemented by jsdom, so we use
// textContent(). The result should be the same, since
Expand Down Expand Up @@ -464,20 +464,20 @@ export function sigmoid(x) {
export function isVisible(fnodeOrElement) {
// This could be 5x more efficient if https://github.com/w3c/csswg-drafts/issues/4122 happens.
const element = toDomElement(fnodeOrElement);
// Avoid reading ``display: none`` due to Bug 1381071
const elementRect = element.getBoundingClientRect();
if (elementRect.width === 0 && elementRect.height === 0) {
const elementStyle = getComputedStyle(element);
// Alternative to reading ``display: none`` due to Bug 1381071.
if (elementRect.width === 0 && elementRect.height === 0 && elementStyle.overflow !== 'hidden') {
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Shouldn't this be elementStyle.overflow === 'hidden'? As you say below, "Zero-sized ancestors don’t make descendants hidden unless the descendant has overflow: hidden".

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The check you're thinking of is done inside the for loop below. This first check is a proxy for checking display: none, for which just checking width and height === 0 is not sufficient as I learned while working on #122 .

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Ah, so this is a check strictly for the visibility of the element passed in, not any of its descendents. A child, for example, could still be visible. Callers will have to be aware of this. That'd be worth documenting in the doclet, as I wasn't front-end-savvy enough to realize it.

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Hm... I'm not sure I follow what you want me to document. In general, this method is to check if the element passed in is visible. It doesn't make any claims about that element's descendants.

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We discussed this synchronously, and we're just going to leave off any additional comments for now.

return false;
}
const elementStyle = getComputedStyle(element);
if (elementStyle.visibility === 'hidden') {
return false;
}
// Check if the element is off-screen
// Check if the element is off-screen:
const frame = element.ownerDocument.defaultView;
if (elementRect.x + elementRect.width < 0
|| (elementRect.y + elementRect.height) < 0
|| (elementRect.x > frame.innerWidth || elementRect.y > frame.innerHeight)
if (elementRect.x + elementRect.width < 0 ||
elementRect.y + elementRect.height < 0 ||
elementRect.x > frame.innerWidth || elementRect.y > frame.innerHeight
) {
return false;
}
Expand All @@ -488,14 +488,14 @@ export function isVisible(fnodeOrElement) {
return false;
}
if (style.display === 'contents') {
// display: contents elements have no box themselves, but children are
// ``display: contents`` elements have no box themselves, but children are
// still rendered.
continue;
}
const rect = isElement ? elementRect : ancestor.getBoundingClientRect();
if ((rect.width === 0 || rect.height === 0) && elementStyle.overflow === 'hidden') {
// Zero-sized ancestors don’t make descendants hidden unless the descendant
// has overflow: hidden
// has ``overflow: hidden``.
return false;
}
}
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