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Fix: Update CSS background URL regex to prevent empty URLs #67

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Fix: Update CSS background URL regex to prevent empty URLs #67

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0a25afb
Fix: Update CSS background URL regex to prevent empty URLs
Miraeld Nov 26, 2025
c6d4fac
refactor: Apply Copilot suggestions for regex and validation
Miraeld Nov 26, 2025
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36 changes: 29 additions & 7 deletions src/BeaconLcp.js
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Original file line number Diff line number Diff line change
Expand Up @@ -94,7 +94,7 @@ class BeaconLcp {
current_src: ""
};

const css_bg_url_rgx = /url\(\s*?['"]?\s*?(.+?)\s*?["']?\s*?\)/ig;
const css_bg_url_rgx = /url\(\s*(['"]?)(.*?)\1\s*\)/ig;

if (nodeName === "img" && element.srcset) {
element_info.type = "img-srcset";
Expand All @@ -106,22 +106,38 @@ class BeaconLcp {
element_info.type = "img";
element_info.src = element.src;
element_info.current_src = element.currentSrc;
// Return null if src is empty or just whitespace
if (!element_info.src || !element_info.src.trim()) {
return null;
}
} else if (nodeName === "video") {
element_info.type = "img";
const source = element.querySelector('source');
element_info.src = element.poster || (source ? source.src : '');
element_info.current_src = element_info.src;
// Return null if src is empty or just whitespace
if (!element_info.src || !element_info.src.trim()) {
return null;
}
} else if (nodeName === "svg") {
const imageElement = element.querySelector('image');
if (imageElement) {
const href = imageElement.getAttribute('href') || '';
if (!href || !href.trim()) {
return null;
}
element_info.type = "img";
element_info.src = imageElement.getAttribute('href') || '';
element_info.src = href;
element_info.current_src = element_info.src;
}
} else if (nodeName === "picture") {
element_info.type = "picture";
const img = element.querySelector('img');
element_info.src = img ? img.src : "";
// Return null if src is empty or just whitespace
if (!element_info.src || !element_info.src.trim()) {
return null;
}
element_info.sources = Array.from(element.querySelectorAll('source')).map(source => ({
srcset: source.srcset || '',
media: source.media || '',
Expand Down Expand Up @@ -149,10 +165,10 @@ class BeaconLcp {
}

const matches = [...full_bg_prop.matchAll(css_bg_url_rgx)];
element_info.bg_set = matches.map(m => m[1] ? { src: m[1].trim() + (m[2] ? " " + m[2].trim() : "") } : {});
if (element_info.bg_set.every(item => item.src === "")) {
element_info.bg_set = matches.map(m => m[1] ? { src: m[1].trim() } : {});
}
// m[2] is the URL content (m[1] is the quote character)
element_info.bg_set = matches
.map(m => m[2] ? { src: m[2].trim() } : {})
.filter(item => item.src && item.src !== "");

if (element_info.bg_set.length <= 0) {
return null;
Expand All @@ -171,7 +187,13 @@ class BeaconLcp {

_initWithFirstElementWithInfo(elements) {
const firstElementWithInfo = elements.find(item => {
return item.elementInfo !== null && (item.elementInfo.src || item.elementInfo.srcset);
if (!item.elementInfo) {
return false;
}
const hasSrc = item.elementInfo.src &&
(typeof item.elementInfo.src === 'string' ? item.elementInfo.src.trim() !== '' : Array.isArray(item.elementInfo.src));
const hasSrcset = item.elementInfo.srcset && item.elementInfo.srcset.trim();
return hasSrc || hasSrcset;
});

if (!firstElementWithInfo) {
Expand Down
139 changes: 139 additions & 0 deletions test/BeaconLcp.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -83,6 +83,31 @@ describe('BeaconManager', function() {

assert.strictEqual(beacon.performanceImages.length, 0);
});

it('should skip elements with empty src strings', function() {
const elements = [
{ element: { nodeName: 'img' }, elementInfo: { type: 'img', src: '' } }, // empty src
{ element: { nodeName: 'img' }, elementInfo: { type: 'img', src: ' ' } }, // whitespace src
{ element: { nodeName: 'img' }, elementInfo: { type: 'img', src: 'http://example.com/valid.jpg' } },
];

beacon._initWithFirstElementWithInfo(elements);

assert.strictEqual(beacon.performanceImages.length, 1);
assert.strictEqual(beacon.performanceImages[0].src, 'http://example.com/valid.jpg');
assert.strictEqual(beacon.performanceImages[0].label, 'lcp');
});

it('should handle elements with srcset instead of src', function() {
const elements = [
{ element: { nodeName: 'img' }, elementInfo: { type: 'img-srcset', src: '', srcset: 'image-320w.jpg 320w, image-640w.jpg 640w' } },
];

beacon._initWithFirstElementWithInfo(elements);

assert.strictEqual(beacon.performanceImages.length, 1);
assert.strictEqual(beacon.performanceImages[0].srcset, 'image-320w.jpg 320w, image-640w.jpg 640w');
});
});

describe('#_getElementInfo()', function() {
Expand All @@ -95,6 +120,120 @@ describe('BeaconManager', function() {

assert.strictEqual(elementInfo, null);
});

it('should return null for img elements with empty src', function() {
const element = {
nodeName: 'img',
src: '',
currentSrc: ''
};

const elementInfo = beacon._getElementInfo(element);

assert.strictEqual(elementInfo, null);
});

it('should return null for img elements with whitespace-only src', function() {
const element = {
nodeName: 'img',
src: ' ',
currentSrc: ' '
};

const elementInfo = beacon._getElementInfo(element);

assert.strictEqual(elementInfo, null);
});

it('should return null for svg image elements with empty href', function() {
const imageElement = {
getAttribute: sinon.stub().returns('')
};
const element = {
nodeName: 'svg',
querySelector: sinon.stub().returns(imageElement)
};

const elementInfo = beacon._getElementInfo(element);

assert.strictEqual(elementInfo, null);
assert.strictEqual(element.querySelector.calledWith('image'), true);
assert.strictEqual(imageElement.getAttribute.calledWith('href'), true);
});

it('should return null for svg image elements with whitespace-only href', function() {
const imageElement = {
getAttribute: sinon.stub().returns(' \n\t ')
};
const element = {
nodeName: 'svg',
querySelector: sinon.stub().returns(imageElement)
};

const elementInfo = beacon._getElementInfo(element);

assert.strictEqual(elementInfo, null);
});

it('should return valid element info for svg image elements with non-empty href', function() {
const imageElement = {
getAttribute: sinon.stub().returns('https://example.com/image.svg')
};
const element = {
nodeName: 'svg',
querySelector: sinon.stub().returns(imageElement)
};

const elementInfo = beacon._getElementInfo(element);

assert.notStrictEqual(elementInfo, null);
assert.strictEqual(elementInfo.type, 'img');
assert.strictEqual(elementInfo.src, 'https://example.com/image.svg');
});

it('should return null for video elements with empty poster and no source', function() {
const element = {
nodeName: 'video',
poster: '',
querySelector: sinon.stub().returns(null)
};

const elementInfo = beacon._getElementInfo(element);

assert.strictEqual(elementInfo, null);
});

it('should return null for picture elements with empty img src', function() {
const imgElement = {
src: ''
};
const element = {
nodeName: 'picture',
querySelector: sinon.stub().returns(imgElement),
querySelectorAll: sinon.stub().returns([])
};

const elementInfo = beacon._getElementInfo(element);

assert.strictEqual(elementInfo, null);
});

it('should return valid element info for picture elements with non-empty img src', function() {
const imgElement = {
src: 'https://example.com/image.jpg'
};
const element = {
nodeName: 'picture',
querySelector: sinon.stub().returns(imgElement),
querySelectorAll: sinon.stub().returns([])
};

const elementInfo = beacon._getElementInfo(element);

assert.notStrictEqual(elementInfo, null);
assert.strictEqual(elementInfo.type, 'picture');
assert.strictEqual(elementInfo.src, 'https://example.com/image.jpg');
});
});

describe('#_generateLcpCandidates()', function() {
Expand Down