babel/packages/babel-plugin-transform-react-constant-elements

@babel/plugin-transform-react-constant-elements

Treat React JSX elements as value types and hoist them to the highest scope.

This plugin can speed up reconciliation and reduce garbage collection pressure by hoisting React elements to the highest possible scope, preventing multiple unnecessary reinstantiations.

Example

In

const Hr = () => {
  return <hr className="hr" />;
};

Out

const _ref = <hr className="hr" />;

const Hr = () => {
  return _ref;
};

Deopts

• Spread Operator

  <div {...foobar} />
  

• Refs

  <div ref="foobar" />
  <div ref={node => this.node = node} />
  

• Mutable Properties

See https://github.com/facebook/react/issues/3226 for more on this

<div width={{width: 100}} />

Installation

npm install --save-dev @babel/plugin-transform-react-constant-elements

Usage

Via .babelrc (Recommended)

.babelrc

{
  "plugins": ["@babel/plugin-transform-react-constant-elements"]
}

Options

allowMutablePropsOnTags

Array<string>, defaults to []

If you are using a particular library (like react-intl) that uses object properties, and you are sure that the element won't modify its own props, you can whitelist the element so that objects are allowed.

This will skip the Mutable Properties deopt.

{
  "plugins": [
    ["@babel/plugin-transform-react-constant-elements", {"allowMutablePropsOnTags": ["FormattedMessage"]}],
  ]
}

Via CLI

babel --plugins @babel/plugin-transform-react-constant-elements script.js

Via Node API

require("@babel/core").transform("code", {
  plugins: ["@babel/plugin-transform-react-constant-elements"]
});

References

• [facebook/react#3226] Optimizing Compiler: Reuse Constant Value Types like ReactElement