b8a0240aaf
Summary: Pull Request resolved: https://github.com/facebook/yoga/pull/1310 Emscripten normally compiles a binary into a `.js` file and a `.wasm` file. The `.js` file contains a shim to load the WebAssembly file for the target platform, along with passing some environment information to the underlying assembly. Under Node this would use APIs like `fs.readFile` and its WebAssembly APIs to load the binary. In a browser, APIs like `instantiateStreaming` are used to start downloading and compiling the binary at the same time. This format creates many, many, headaches, and manual bundler configuration. E.g. we must tell Webpack to treat WASM files as auxilary files instead of WebAssembly, cannot use Emscripten's loader directly, and would need to add more variants of the binary, since (or Node polyfills in the browser) `-s ENVIRONMENT='web,node'` emits code that looks like `if (isNode) {require('fs')}`. This change makes us instead pack the WebAssembly as base64 inline with the JS loader. This adds a size penalty, and means we cannot start async compilation until the entire file is present, but should work out of the box when using different bundlers and configurations, and the size is small enough where it likely makes sense to inline into the bundle anyway. There is a [proposal for integration of WebAssembly and ES Modules](https://github.com/WebAssembly/esm-integration/tree/main/proposals/esm-integration) that Node has experimental support for, and bundlers are veering towards supporting. It is the eventual solution we should target, but does not seem mature enough yet. E.g. WebPack [does not support](https://github.com/webpack/webpack/issues/11893) WebAssembly import objects, and will instead try to import each of the named imports as modules. Reviewed By: rozele Differential Revision: D46884398 fbshipit-source-id: a1c93c122c255b913f426bfb6bdb38fd9f9dfd41
yoga-layout
This package provides prebuilt JavaScript bindings for the Yoga layout engine. Both WebAssembly and asm.js variants are packaged, with the optimal loaded based on platform.
Usage
The default entrypoint provides an asynchronous loader function to return a Yoga instance.
import {loadYoga, Align} from 'yoga-layout';
const Yoga = await loadYoga();
const node = Yoga.Node.create();
node.setAlignContent(Align.Center);
An alternative synchronous API is provided for compatibility, but requires using asm.js in browsers instead of WebAssembly, leading to worse performance and larger assets.
import Yoga, {Align} from 'yoga-layout/sync';
const node = Yoga.Node.create();
node.setAlignContent(Align.Center);
Objects created by Yoga.<>.create() are not automatically garbage collected and should be freed once they are no longer in use.
// Free a config
config.free();
// Free a tree of Nodes
node.freeRecursive();
// Free a single Node
node.free();
Selecting WebAssembly or asm.js
For better performance and smaller packages, WebAssembly is preferred to asm.js where available. yoga-layout tries to provide the right default using export maps so that platforms which can take advantage of WebAssembly use it by default.
A specific entrypoint may be specified on platforms which do not understand export conditions.
import {loadYoga} from 'yoga-layout/wasm-async';
Contributing
Requirements
- Emscripten SDK
- CMake >= 3.13
- (Optional) ninja, for faster builds
Building
git clone https://github.com/facebook/yoga.git
cd yoga/javascript
yarn install
yarn build
Testing
# Build and test all entrypoints
yarn test
# Build and test a specific entrypoint
yarn test:asmjs-sync