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

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

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

const WithChildren = (props) => {
  return <div className={props.className}>
    <hr />
  </div>;
}

Out

JSX
var _hr, _hr2;

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

const WithChildren = (props) => {
  return <div className={props.className}>
    {_hr2 || (_hr2 = <hr />)}
  </div>;
}

Deopts

  • Spread Operator

    JSX
    <div {...foobar} />

  • Refs

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

  • Mutable Properties

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

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

Installation​

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

Usage​

babel.config.json
{
  "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 permit objects to be allowed for specific elements.

This will skip the Mutable Properties deopt.

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

You can read more about configuring plugin options here

Via CLI​

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

Via Node API​

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

References​