26 lines
1.5 KiB
TypeScript
26 lines
1.5 KiB
TypeScript
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import { CLSMetric, MetricRatingThresholds, ReportOpts } from './types.js';
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/** Thresholds for CLS. See https://web.dev/articles/cls#what_is_a_good_cls_score */
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export declare const CLSThresholds: MetricRatingThresholds;
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/**
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* Calculates the [CLS](https://web.dev/articles/cls) value for the current page and
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* calls the `callback` function once the value is ready to be reported, along
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* with all `layout-shift` performance entries that were used in the metric
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* value calculation. The reported value is a `double` (corresponding to a
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* [layout shift score](https://web.dev/articles/cls#layout_shift_score)).
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*
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* If the `reportAllChanges` configuration option is set to `true`, the
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* `callback` function will be called as soon as the value is initially
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* determined as well as any time the value changes throughout the page
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* lifespan.
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*
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* _**Important:** CLS should be continually monitored for changes throughout
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* the entire lifespan of a page—including if the user returns to the page after
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* it's been hidden/backgrounded. However, since browsers often [will not fire
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* additional callbacks once the user has backgrounded a
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* page](https://developer.chrome.com/blog/page-lifecycle-api/#advice-hidden),
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* `callback` is always called when the page's visibility state changes to
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* hidden. As a result, the `callback` function might be called multiple times
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* during the same page load._
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*/
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export declare const onCLS: (onReport: (metric: CLSMetric) => void, opts?: ReportOpts) => void;
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