babel-plugin-hoist-facc

Note: This plugin was not intensively tested and was not actively used in production. Use it at one's own risk.

Treat FACC as value types and hoist them to the highest scope

Install

Using npm:

npm install --save-dev @babel/core babel-plugin-hoist-facc

or using yarn:

yarn add @babel/core babel-plugin-hoist-facc --dev

What problem it solves?

It solves the problem of rendering optimization, which comes with FaCC pattern. In a few words: Function as Child Component can't be optimized by shouldComponentUpdate because the child function is always changes on render.

This plugin hoist the child function to highest possible scope to prevent its changes.

Example

class extends React.Component {
  render() {
    return <FaCC>{() => <div />}</FaCC>; // arrow function changes on each render
  }
}

⇩⇩⇩

var _ref = () => <div />;

class extends React.Component {
  render() {
    return <FaCC>{_ref}</FaCC>; // now it's constant
  }
}

Options

| Option | Defaults | Description | | ------------------ | :------: | :--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | unsafeHoistInClass | false | When true, enables the hoisting of FaCC children function, which refers to this, to the class constructor. Potentially it is unsafe due to context losing issue, but in regular React life this shouldt happens. See example below. | | warnIfCantHoist | false | When true, display a warnings about child functions that couldn't be hoisted. | | loose | false | When true`, class properties are compiled to use an assignment expression instead of Object.defineProperty. |

More examples

["hoist-facc", { unsafeHoistInClass: true, loose: true }]

class extends React.Component {
  handleClick = () => {};

  render() {
    return <FaCC>{() => <button onClick={this.handleClick} />}</FaCC>;
  }
}

⇩⇩⇩

class extends React.Component {
  constructor(...args) {
    super(...args);

    this.handleClick = () => {};
    this._ref = () => <button onClick={this.handleClick} />;
  }

  render() {
    return <FaCC>{this._ref}</FaCC>;
  }
}

Pitfalls

There some cases it can't be hoisted automagically.

class extends React.Component {
  render() {
    const { id, label } = this.props;

    return <FaCC>{() => <div id={id}>{label}</div>}</FaCC>;
  }
}

The above code will not be transformed, because the id and label from the higher scope is used inside FaCC. You should proxy the props to the child function or access props directly trought this keyword to avoid this.

class extends React.Component {
  render() {
    return (
      <FaCC {...this.props}>
        {({ id }) => (
          <div id={id}>{this.props.label}</div>
        )}
      </FaCC>
    );
  }
}