Initial Commit

node_modules/web-vitals/dist/modules/attribution/onCLS.js

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+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import { getLoadState } from '../lib/getLoadState.js';
+import { getSelector } from '../lib/getSelector.js';
+import { onCLS as unattributedOnCLS } from '../onCLS.js';
+const getLargestLayoutShiftEntry = (entries) => {
+    return entries.reduce((a, b) => (a && a.value > b.value ? a : b));
+};
+const getLargestLayoutShiftSource = (sources) => {
+    return sources.find((s) => s.node && s.node.nodeType === 1) || sources[0];
+};
+const attributeCLS = (metric) => {
+    // Use an empty object if no other attribution has been set.
+    let attribution = {};
+    if (metric.entries.length) {
+        const largestEntry = getLargestLayoutShiftEntry(metric.entries);
+        if (largestEntry && largestEntry.sources && largestEntry.sources.length) {
+            const largestSource = getLargestLayoutShiftSource(largestEntry.sources);
+            if (largestSource) {
+                attribution = {
+                    largestShiftTarget: getSelector(largestSource.node),
+                    largestShiftTime: largestEntry.startTime,
+                    largestShiftValue: largestEntry.value,
+                    largestShiftSource: largestSource,
+                    largestShiftEntry: largestEntry,
+                    loadState: getLoadState(largestEntry.startTime),
+                };
+            }
+        }
+    }
+    // Use Object.assign to set property to keep tsc happy.
+    const metricWithAttribution = Object.assign(metric, { attribution });
+    return metricWithAttribution;
+};
+/**
+ * Calculates the [CLS](https://web.dev/articles/cls) value for the current page and
+ * calls the `callback` function once the value is ready to be reported, along
+ * with all `layout-shift` performance entries that were used in the metric
+ * value calculation. The reported value is a `double` (corresponding to a
+ * [layout shift score](https://web.dev/articles/cls#layout_shift_score)).
+ *
+ * If the `reportAllChanges` configuration option is set to `true`, the
+ * `callback` function will be called as soon as the value is initially
+ * determined as well as any time the value changes throughout the page
+ * lifespan.
+ *
+ * _**Important:** CLS should be continually monitored for changes throughout
+ * the entire lifespan of a page—including if the user returns to the page after
+ * it's been hidden/backgrounded. However, since browsers often [will not fire
+ * additional callbacks once the user has backgrounded a
+ * page](https://developer.chrome.com/blog/page-lifecycle-api/#advice-hidden),
+ * `callback` is always called when the page's visibility state changes to
+ * hidden. As a result, the `callback` function might be called multiple times
+ * during the same page load._
+ */
+export const onCLS = (onReport, opts) => {
+    unattributedOnCLS((metric) => {
+        const metricWithAttribution = attributeCLS(metric);
+        onReport(metricWithAttribution);
+    }, opts);
+};