88 lines
4.1 KiB
Markdown
88 lines
4.1 KiB
Markdown
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# Hermes Profile Transformer
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<p align="center">
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<img alt="npm" src="https://img.shields.io/npm/v/hermes-profile-transformer">
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<img alt="node-current" src="https://img.shields.io/node/v/hermes-profile-transformer">
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<img alt="npm bundle size" src="https://img.shields.io/bundlephobia/min/hermes-profile-transformer">
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<img alt="NPM" src="https://img.shields.io/npm/l/hermes-profile-transformer">
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<img alt="npm type definitions" src="https://img.shields.io/npm/types/hermes-profile-transformer">
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</p>
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Visualize Facebook's [Hermes JavaScript runtime](https://github.com/facebook/hermes) profile traces in Chrome Developer Tools.
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## Overview
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The Hermes runtime, used by React Native for Android, is able to output [Chrome Trace Events](https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview) in JSON Object Format.
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This TypeScript package converts Hermes CPU profiles to Chrome Developer Tools compatible JSON Array Format, and enriches it with line and column numbers and event categories from JavaScript source maps.
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## Usage
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If you're using `hermes-profile-transformer` to debug React Native Android applications, you can use the [React Native CLI](https://github.com/react-native-community/cli) `react-native profile-hermes` command, which uses this package to convert the downloaded Hermes profiles automatically.
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### As a standalone package
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```js
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const transformer = require('hermes-profile-transformer').default;
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const { promises } = require('fs');
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const hermesCpuProfilePath = './testprofile.cpuprofile';
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const sourceMapPath = './index.map';
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const sourceMapBundleFileName = 'index.bundle.js';
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transformer(
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// profile path is required
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hermesCpuProfilePath,
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// source maps are optional
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sourceMap,
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sourceMapBundleFileName
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)
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.then(events => {
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// write converted trace to a file
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return promises.writeFile(
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'./chrome-supported.json',
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JSON.stringify(events, null, 2),
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'utf-8'
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);
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})
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.catch(err => {
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console.log(err);
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});
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```
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## Creating Hermes CPU Profiles
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## Opening converted profiles in Chrome Developer Tools
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Open Developer Tools in Chrome, navigate to the **Performance** tab, and use the **Load profile...** feature.
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## API
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### transformer(profilePath: string, sourceMapPath?: string, bundleFileName?: string)
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#### Parameters
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| Parameter | Type | Required | Description |
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| -------------- | ------ | -------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| profilePath | string | Yes | Path to a JSON-formatted `.cpuprofile` file created by the Hermes runtime |
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| sourceMapPath | string | No | Path to a [source-map](https://www.npmjs.com/package/source-map) compatible Source Map file |
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| bundleFileName | string | No | If `sourceMapPath` is provided, you need to also provide the name of the JavaScript bundle file that the source map applies to. This file does not need to exist on disk. |
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#### Returns
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`Promise<DurationEvent[]>`, where `DurationEvent` is as defined in [EventInterfaces.ts](src/types/EventInterfaces.ts).
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## Resources
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- [Using Hermes with React Native](https://reactnative.dev/docs/hermes).
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- [Chrome Trace Event Format](https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview). Hermes uses the JSON Object format.
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- [Measuring JavaScript performance in Chrome](https://developers.google.com/web/tools/chrome-devtools/evaluate-performance/reference)
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## LICENSE
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[MIT](LICENSE)
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