new_audit: add Max Potential FID to JSON

lighthouse-cli/test/cli/__snapshots__/index-test.js.snap

@@ -42,6 +42,9 @@ Object {
     Object {
       "path": "metrics/estimated-input-latency",
     },
+    Object {
+      "path": "metrics/max-potential-fid",
+    },
     Object {
       "path": "errors-in-console",
     },
@@ -682,6 +685,10 @@ Object {
           "id": "estimated-input-latency",
           "weight": 0,
         },
+        Object {
+          "id": "max-potential-fid",
+          "weight": 0,
+        },
         Object {
           "group": "load-opportunities",
           "id": "render-blocking-resources",

lighthouse-core/audits/metrics/max-potential-fid.js

@@ -0,0 +1,76 @@
+/**
+ * @license Copyright 2018 Google Inc. All Rights Reserved.
+ * 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 http://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.
+ */
+'use strict';
+
+const Audit = require('../audit');
+const ComputedFid = require('../../computed/metrics/max-potential-fid.js');
+const i18n = require('../../lib/i18n/i18n');
+
+const UIStrings = {
+  /** The name of the metric "Maximum Potential First Input Delay" that marks the maximum estimated time between the page receiving input (a user clicking, tapping, or typing) and the page responding. Shown to users as the label for the numeric metric value. Ideally fits within a ~40 character limit. */
+  title: 'Max Potential FID',
+  /** Description of the Estimated Input Latency metric that estimates the amount of time, in milliseconds, that the app takes to respond to user input. This description is displayed within a tooltip when the user hovers on the metric name to see more. No character length limits. 'Learn More' becomes link text to additional documentation. */
+  description: 'The potential First Input Delay that your users could experience is the ' +
+      'duration, in milliseconds, of the longest task.',
+};
+
+const str_ = i18n.createMessageInstanceIdFn(__filename, UIStrings);
+
+/**
+ * @fileoverview This metric is the duration of the longest task after FCP. It is meant to capture
+ * the worst case First Input Delay that a user might experience.
+ * Tasks before FCP are excluded because it is unlikely that the user will try to interact with a page before it has painted anything.
+ */
+class MaxPotentialFID extends Audit {
+  /**
+   * @return {LH.Audit.Meta}
+   */
+  static get meta() {
+    return {
+      id: 'max-potential-fid',
+      title: str_(UIStrings.title),
+      description: str_(UIStrings.description),
+      scoreDisplayMode: Audit.SCORING_MODES.NUMERIC,
+      requiredArtifacts: ['traces'],
+    };
+  }
+
+  /**
+   * @return {LH.Audit.ScoreOptions}
+   */
+  static get defaultOptions() {
+    return {
+      // see https://www.desmos.com/calculator/g3nf1ehtnk
+      scorePODR: 100,
+      scoreMedian: 250,
+    };
+  }
+
+  /**
+   * @param {LH.Artifacts} artifacts
+   * @param {LH.Audit.Context} context
+   * @return {Promise<LH.Audit.Product>}
+   */
+  static async audit(artifacts, context) {
+    const trace = artifacts.traces[Audit.DEFAULT_PASS];
+    const devtoolsLog = artifacts.devtoolsLogs[Audit.DEFAULT_PASS];
+    const metricComputationData = {trace, devtoolsLog, settings: context.settings};
+    const metricResult = await ComputedFid.request(metricComputationData, context);
+
+    return {
+      score: Audit.computeLogNormalScore(
+        metricResult.timing,
+        context.options.scorePODR,
+        context.options.scoreMedian
+      ),
+      rawValue: metricResult.timing,
+      displayValue: str_(i18n.UIStrings.ms, {timeInMs: metricResult.timing}),
+    };
+  }
+}
+
+module.exports = MaxPotentialFID;
+module.exports.UIStrings = UIStrings;

lighthouse-core/computed/metrics/lantern-max-potential-fid.js

@@ -0,0 +1,98 @@
+/**
+ * @license Copyright 2018 Google Inc. All Rights Reserved.
+ * 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 http://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.
+ */
+'use strict';
+
+const makeComputedArtifact = require('../computed-artifact.js');
+const LanternMetricArtifact = require('./lantern-metric');
+const BaseNode = require('../../lib/dependency-graph/base-node');
+const LanternFirstContentfulPaint = require('./lantern-first-contentful-paint.js');
+
+/** @typedef {BaseNode.Node} Node */
+
+class LanternMaxPotentialFID extends LanternMetricArtifact {
+  /**
+   * @return {LH.Gatherer.Simulation.MetricCoefficients}
+   */
+  static get COEFFICIENTS() {
+    return {
+      intercept: 0,
+      optimistic: 0.5,
+      pessimistic: 0.5,
+    };
+  }
+
+  /**
+   * @param {Node} dependencyGraph
+   * @return {Node}
+   */
+  static getOptimisticGraph(dependencyGraph) {
+    return dependencyGraph;
+  }
+
+  /**
+   * @param {Node} dependencyGraph
+   * @return {Node}
+   */
+  static getPessimisticGraph(dependencyGraph) {
+    return dependencyGraph;
+  }
+
+  /**
+   * @param {LH.Gatherer.Simulation.Result} simulation
+   * @param {Object} extras
+   * @return {LH.Gatherer.Simulation.Result}
+   */
+  static getEstimateFromSimulation(simulation, extras) {
+    // Intentionally use the opposite FCP estimate, a more pessimistic FCP means that more tasks
+    // are excluded from the FID computation, so a higher FCP means lower FID for same work.
+    const fcpTimeInMs = extras.optimistic
+      ? extras.fcpResult.pessimisticEstimate.timeInMs
+      : extras.fcpResult.optimisticEstimate.timeInMs;
+
+    const events = LanternMaxPotentialFID.getEventsAfterFCP(
+      simulation.nodeTimings,
+      fcpTimeInMs
+    );
+
+    return {
+      timeInMs: Math.max(...events.map(evt => evt.duration), 16),
+      nodeTimings: simulation.nodeTimings,
+    };
+  }
+
+  /**
+   * @param {LH.Artifacts.MetricComputationDataInput} data
+   * @param {LH.Audit.Context} context
+   * @return {Promise<LH.Artifacts.LanternMetric>}
+   */
+  static async compute_(data, context) {
+    const fcpResult = await LanternFirstContentfulPaint.request(data, context);
+    return super.computeMetricWithGraphs(data, context, {fcpResult});
+  }
+
+  /**
+   * @param {LH.Gatherer.Simulation.Result['nodeTimings']} nodeTimings
+   * @param {number} fcpTimeInMs
+   */
+  static getEventsAfterFCP(nodeTimings, fcpTimeInMs) {
+    /** @type {Array<{start: number, end: number, duration: number}>} */
+    const events = [];
+    for (const [node, timing] of nodeTimings.entries()) {
+      if (node.type !== BaseNode.TYPES.CPU) continue;
+      if (timing.endTime < fcpTimeInMs) continue;
+
+      events.push({
+        start: timing.startTime,
+        end: timing.endTime,
+        duration: timing.duration,
+      });
+    }
+
+    return events;
+  }
+}
+
+module.exports = makeComputedArtifact(LanternMaxPotentialFID);

lighthouse-core/computed/metrics/max-potential-fid.js

@@ -0,0 +1,45 @@
+/**
+ * @license Copyright 2018 Google Inc. All Rights Reserved.
+ * 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 http://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.
+ */
+'use strict';
+
+const makeComputedArtifact = require('../computed-artifact.js');
+const MetricArtifact = require('./metric');
+const LanternMaxPotentialFID = require('./lantern-max-potential-fid.js');
+const LHError = require('../../lib/lh-error');
+const TracingProcessor = require('../../lib/traces/tracing-processor');
+
+class MaxPotentialFID extends MetricArtifact {
+  /**
+   * @param {LH.Artifacts.MetricComputationData} data
+   * @param {LH.Audit.Context} context
+   * @return {Promise<LH.Artifacts.LanternMetric>}
+   */
+  static computeSimulatedMetric(data, context) {
+    return LanternMaxPotentialFID.request(data, context);
+  }
+
+  /**
+   * @param {LH.Artifacts.MetricComputationData} data
+   * @return {Promise<LH.Artifacts.Metric>}
+   */
+  static computeObservedMetric(data) {
+    const {firstContentfulPaint} = data.traceOfTab.timings;
+    if (!firstContentfulPaint) {
+      throw new LHError(LHError.errors.NO_FCP);
+    }
+
+    const events = TracingProcessor.getMainThreadTopLevelEvents(
+      data.traceOfTab,
+      firstContentfulPaint
+    ).filter(evt => evt.duration >= 1);
+
+    return Promise.resolve({
+      timing: Math.max(...events.map(evt => evt.duration), 16),
+    });
+  }
+}
+
+module.exports = makeComputedArtifact(MaxPotentialFID);

lighthouse-core/config/default-config.js

@@ -144,6 +144,7 @@ const defaultConfig = {
     'screenshot-thumbnails',
     'final-screenshot',
     'metrics/estimated-input-latency',
+    'metrics/max-potential-fid',
     'errors-in-console',
     'time-to-first-byte',
     'metrics/first-cpu-idle',
@@ -328,6 +329,7 @@ const defaultConfig = {
         {id: 'interactive', weight: 5, group: 'metrics'},
         {id: 'first-cpu-idle', weight: 2, group: 'metrics'},
         {id: 'estimated-input-latency', weight: 0, group: 'metrics'},
+        {id: 'max-potential-fid', weight: 0}, // intentionally left out of metrics so it won't be displayed yet
 
         {id: 'render-blocking-resources', weight: 0, group: 'load-opportunities'},
         {id: 'uses-responsive-images', weight: 0, group: 'load-opportunities'},

lighthouse-core/lib/i18n/en-US.json

@@ -691,6 +691,14 @@
     "message": "Time to Interactive",
     "description": "The name of the metric that marks the time at which the page is fully loaded and is able to quickly respond to user input (clicks, taps, and keypresses feel responsive). Shown to users as the label for the numeric metric value. Ideally fits within a ~40 character limit."
   },
+  "lighthouse-core/audits/metrics/max-potential-fid.js | description": {
+    "message": "The potential First Input Delay that your users could experience is the duration, in milliseconds, of the longest task.",
+    "description": "Description of the Estimated Input Latency metric that estimates the amount of time, in milliseconds, that the app takes to respond to user input. This description is displayed within a tooltip when the user hovers on the metric name to see more. No character length limits. 'Learn More' becomes link text to additional documentation."
+  },
+  "lighthouse-core/audits/metrics/max-potential-fid.js | title": {
+    "message": "Max Potential FID",
+    "description": "The name of the metric \"Maximum Potential First Input Delay\" that marks the maximum estimated time between the page receiving input (a user clicking, tapping, or typing) and the page responding. Shown to users as the label for the numeric metric value. Ideally fits within a ~40 character limit."
+  },
   "lighthouse-core/audits/metrics/speed-index.js | description": {
     "message": "Speed Index shows how quickly the contents of a page are visibly populated. [Learn more](https://developers.google.com/web/tools/lighthouse/audits/speed-index).",
     "description": "Description of the Speed Index metric, which summarizes how quickly the page looked visually complete. This is displayed within a tooltip when the user hovers on the metric name to see more. No character length limits. 'Learn More' becomes link text to additional documentation."

lighthouse-core/test/computed/metrics/__snapshots__/max-potential-fid-test.js.snap

@@ -0,0 +1,9 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Metrics: Max Potential FID should compute a simulated value 1`] = `
+Object {
+  "optimistic": 396,
+  "pessimistic": 396,
+  "timing": 396,
+}
+`;

lighthouse-core/test/computed/metrics/max-potential-fid-test.js

@@ -0,0 +1,36 @@
+/**
+ * @license Copyright 2018 Google Inc. All Rights Reserved.
+ * 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 http://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.
+ */
+'use strict';
+
+const assert = require('assert');
+
+const MaxPotentialFID = require('../../../computed/metrics/max-potential-fid.js');
+const trace = require('../../fixtures/traces/progressive-app-m60.json');
+const devtoolsLog = require('../../fixtures/traces/progressive-app-m60.devtools.log.json');
+
+/* eslint-env jest */
+
+describe('Metrics: Max Potential FID', () => {
+  it('should compute a simulated value', async () => {
+    const settings = {throttlingMethod: 'simulate'};
+    const context = {settings, computedCache: new Map()};
+    const result = await MaxPotentialFID.request({trace, devtoolsLog, settings}, context);
+
+    expect({
+      timing: Math.round(result.timing),
+      optimistic: Math.round(result.optimisticEstimate.timeInMs),
+      pessimistic: Math.round(result.pessimisticEstimate.timeInMs),
+    }).toMatchSnapshot();
+  });
+
+  it('should compute an observed value', async () => {
+    const settings = {throttlingMethod: 'provided'};
+    const context = {settings, computedCache: new Map()};
+    const result = await MaxPotentialFID.request({trace, devtoolsLog, settings}, context);
+
+    assert.equal(Math.round(result.timing), 198);
+  });
+});

lighthouse-core/test/results/sample_v2.json

@@ -202,6 +202,15 @@
       "rawValue": 16,
       "displayValue": "20 ms"
     },
+    "max-potential-fid": {
+      "id": "max-potential-fid",
+      "title": "Max Potential FID",
+      "description": "The potential First Input Delay that your users could experience is the duration, in milliseconds, of the longest task.",
+      "score": 0.92,
+      "scoreDisplayMode": "numeric",
+      "rawValue": 122.537,
+      "displayValue": "120 ms"
+    },
     "errors-in-console": {
       "id": "errors-in-console",
       "title": "Browser errors were logged to the console",
@@ -2790,6 +2799,10 @@
           "weight": 0,
           "group": "metrics"
         },
+        {
+          "id": "max-potential-fid",
+          "weight": 0
+        },
         {
           "id": "render-blocking-resources",
           "weight": 0,
@@ -3599,6 +3612,18 @@
         "duration": 100,
         "entryType": "measure"
       },
+      {
+        "startTime": 0,
+        "name": "lh:audit:max-potential-fid",
+        "duration": 100,
+        "entryType": "measure"
+      },
+      {
+        "startTime": 0,
+        "name": "lh:computed:MaxPotentialFID",
+        "duration": 100,
+        "entryType": "measure"
+      },
       {
         "startTime": 0,
         "name": "lh:audit:errors-in-console",
@@ -4416,8 +4441,20 @@
             "timeInMs": 16
           },
           "path": "audits[estimated-input-latency].displayValue"
+        },
+        {
+          "values": {
+            "timeInMs": 122.537
+          },
+          "path": "audits[max-potential-fid].displayValue"
         }
       ],
+      "lighthouse-core/audits/metrics/max-potential-fid.js | title": [
+        "audits[max-potential-fid].title"
+      ],
+      "lighthouse-core/audits/metrics/max-potential-fid.js | description": [
+        "audits[max-potential-fid].description"
+      ],
       "lighthouse-core/audits/time-to-first-byte.js | title": [
         "audits[time-to-first-byte].title"
       ],