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core(image-elements): cache naturalSize results #9818

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merged 3 commits into from
Oct 11, 2019
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core(image-elements): cache naturalSize results #9818

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core(image-elements): cache naturalSize results
paulirish Oct 11, 2019
86048ef
Update lighthouse-core/gather/gatherers/image-elements.js
paulirish Oct 11, 2019
2d01548
lint
paulirish Oct 11, 2019
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11 changes: 11 additions & 0 deletions lighthouse-core/gather/gatherers/image-elements.js
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Original file line number Diff line number Diff line change
Expand Up @@ -130,18 +130,29 @@ function determineNaturalSize(url) {
}

class ImageElements extends Gatherer {
constructor() {
super();
/** @type {Map<string, {naturalWidth: number, naturalHeight: number}>} */
this._naturalSizeCache = new Map();
}

/**
* @param {Driver} driver
* @param {LH.Artifacts.ImageElement} element
* @return {Promise<LH.Artifacts.ImageElement>}
*/
async fetchElementWithSizeInformation(driver, element) {
const url = JSON.stringify(element.src);
if (this._naturalSizeCache.has(url)) {
return Object.assign(element, this._naturalSizeCache.get(url));
}

try {
// We don't want this to take forever, 250ms should be enough for images that are cached
driver.setNextProtocolTimeout(250);
/** @type {{naturalWidth: number, naturalHeight: number}} */
const size = await driver.evaluateAsync(`(${determineNaturalSize.toString()})(${url})`);
this._naturalSizeCache.set(url, size);
return Object.assign(element, size);
} catch (_) {
// determineNaturalSize fails on invalid images, which we treat as non-visible
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