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Support lazy loading
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‎README.md‎

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@@ -68,6 +68,20 @@ Default: `[]`
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Description: *list of extension for which the transformation will be ignored*
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Example: `extensionIgnore: ['svg']` will ignore transformation for images with the `svg` extension
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#### `lazySrcset`
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Type: `String`
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Default: `data-srcset`
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Description: *The attribute used for lazy webp loading. It will be set on created `<source>` to later be processed by external lazy loading library.*
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Example: `lazySrcset: 'my-srcset'` will set `my-srcset` attribute on `<source>`
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#### `lazySrc`
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Type: `String`
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Default: `data-src`
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Description: *The attribute used for lazy webp loading. The original `<img>` may not contain `src` at all, but instead some custom lazy-loading attribute. Or it may contain just a placeholder image inside `src` which shouldn't be used for webp conversion. `lazySrc` will define a custom attribute name to look at when processing your lazy loaded images. Note that `lazySrcset` is still needed even if `<img>` has only `lazySrc` defined, because `srcset` is the mechanism for defining a source file for the `<source>`. See `lazySrcset` option description.*
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Example: `lazySrc: 'my-src'` will convert an image inside `my-src` attribute, instead of regular `src`.
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### License [MIT](LICENSE)
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[npm]: https://img.shields.io/npm/v/posthtml-webp.svg

‎lib/index.js‎

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@@ -17,11 +17,21 @@ module.exports = function (options) {
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options.replaceExtension = false
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}
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if (options.lazySrc === undefined) {
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options.lazySrc = 'data-src'
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}
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if (options.lazySrcset === undefined) {
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options.lazySrcset = 'data-srcset'
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}
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return function posthtmlWebp (tree) {
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tree.match([{ tag: 'img' }, { tag: 'amp-img' }], function (imgNode) {
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if (imgNode.skip) return imgNode
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var classes = (imgNode.attrs && imgNode.attrs.class && imgNode.attrs.class.split(' ')) || []
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var extension = imgNode.attrs.src.split('.').pop()
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// Extract extension from lazy loading attribute, because it always contains the right image. (`src` can contain "preview")
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// Use `src` if there are no lazy loading attributes.
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var extension = (imgNode.attrs[options.lazySrc] || imgNode.attrs[options.lazySrcset] || imgNode.attrs.src || imgNode.attrs.srcset).split('.').pop().split(/\s+/)[0]
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var isIgnoredByClass = options.classIgnore.filter(className => classes.includes(className)).length > 0
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var isIgnoredByExtension = options.extensionIgnore.filter(fileExtension => fileExtension === extension).length > 0
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var isIgnore = isIgnoredByClass || isIgnoredByExtension
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function getPicture (imgNode, options) {
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imgNode.skip = true
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// set <source> `srcset` to <img> `srcset`, if present; otherwise — use <img> `src`
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var srcset = (imgNode.attrs.srcset || imgNode.attrs.src)
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var srcset = (imgNode.attrs.srcset || imgNode.attrs[options.lazySrcset] || imgNode.attrs[options.lazySrc] || imgNode.attrs.src)
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.split(',')
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.filter(Boolean)
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.map(value => {
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})
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.join(', ')
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var sourceAttrs = {
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type: 'image/webp'
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}
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sourceAttrs[imgNode.attrs[options.lazySrcset] || imgNode.attrs[options.lazySrc] ? options.lazySrcset : 'srcset'] = srcset
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return {
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tag: 'picture',
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content: [
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{
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tag: 'source',
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attrs: {
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type: 'image/webp',
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srcset
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}
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attrs: sourceAttrs
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},
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imgNode
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]

‎test/fixtures/lazy.expected.html‎

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<!doctype html>
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<html>
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<body>
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<picture><source type="image/webp" data-srcset="photo.webp"><img data-src="photo.jpg"></picture>
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<picture><source type="image/webp" data-srcset="photo.webp"><img data-src="photo.jpg" src="low-quality-preview.jpg"></picture>
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<picture><source type="image/webp" data-srcset="photo-lg.webp 1000w, photo-md.webp 500w, photo-sm.webp 250w"><img data-srcset="photo-lg.jpg 1000w, photo-md.jpg 500w, photo-sm.jpg 250w"></picture>
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<picture><source type="image/webp" data-srcset="photo-lg.webp 1000w, photo-md.webp 500w, photo-sm.webp 250w"><img data-srcset="photo-lg.jpg 1000w, photo-md.jpg 500w, photo-sm.jpg 250w" src="low-quality-preview.jpg"></picture>
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<picture><source type="image/webp" data-srcset="photo-lg.webp 1000w, photo-md.webp 500w, photo-sm.webp 250w"><img data-srcset="photo-lg.jpg 1000w, photo-md.jpg 500w, photo-sm.jpg 250w" data-src="photo.jpg"></picture>
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<picture><source type="image/webp" data-srcset="photo-lg.webp 1000w, photo-md.webp 500w, photo-sm.webp 250w"><img data-srcset="photo-lg.jpg 1000w, photo-md.jpg 500w, photo-sm.jpg 250w" data-src="photo.jpg" src="low-quality-preview.jpg"></picture>
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</body>
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</html>

‎test/fixtures/lazy.html‎

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<!doctype html>
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<html>
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<body>
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<img data-src="photo.jpg">
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<img data-src="photo.jpg" src="low-quality-preview.jpg">
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<img data-srcset="photo-lg.jpg 1000w, photo-md.jpg 500w, photo-sm.jpg 250w">
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<img data-srcset="photo-lg.jpg 1000w, photo-md.jpg 500w, photo-sm.jpg 250w" src="low-quality-preview.jpg">
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<img data-srcset="photo-lg.jpg 1000w, photo-md.jpg 500w, photo-sm.jpg 250w" data-src="photo.jpg">
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<img data-srcset="photo-lg.jpg 1000w, photo-md.jpg 500w, photo-sm.jpg 250w" data-src="photo.jpg" src="low-quality-preview.jpg">
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</body>
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</html>

‎test/test.js‎

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})
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})
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test('Lazy attributes', (t) => {
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return compare(t, 'lazy', {
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replaceExtension: true
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})
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})
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function compare (t, name, options) {
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const html = readFileSync(path.join(fixtures, `${name}.html`), 'utf8')
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const expected = readFileSync(path.join(fixtures, `${name}.expected.html`), 'utf8')

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