jsx-compress-loader

JSX optimization webpack loader

What it does

Replaces React.createElement by a local variable, thus reduce "number of characters" per React Element from 17 to 1, as long local variable would be uglified.

"a.b.createElement".length === 17, "React.default.createElement".length === 27. Usually - about 23

That is not a problem for Preact or Inferno, only to "default" React, as long only React has got "long element creation". See this tweet from Dan Abramov, to find more about it.

This technique also is almost NOT affecting gzipped size, only the real amount of js code, browser has to parse.

Bonus

This also removes object property access (ie React.createElement), thus:

• speeding up Chrome by 5%
• speeding up Safari 11 by 15%
• speeding up Safari 12 by 35%
• not speeding up Mobile Safari 12(iPhone XS)
• here is the test

Would it help?

Just open your bundle, and count createElement inside. Or open any page, and count closing tags </. Next multiply by 22. Result is - amount of bytes you would remove from your bundle. For free.

Usage

Just add this webpack loader AFTER all other.

• after ts
• after js
• after svg -> react -> babel -> js
• and dont forget to apply it to node_modules as well.

in terms of webpack configuration - "after" goes "before", ie top-most loader is the "last" one.

Only for ESM modules!

babel "modules" should be "false" - you already should have it, for proper tree-shaking, and this is what this library is counting on.

As separate loader

rules: [
  {
    test: /\.js$/, // for any js file in your project
    use: 'jsx-compress-loader',
  },
  {
    test: /\.js$/,
    exclude: /node_modules/,
    use: 'babel-loader',    
  },
];

As chained loader

rules: [
  {
    test: /\.js$/, // paired with babel loader
    exclude: /node_modules/,
    use: [    
      'jsx-compress-loader'
      'babel-loader',
    ],
  },
];

Other ways

• babel-plugin-transform-react-inline-elements would inline "createElement", achieving almost the same result
• babel-plugin-transform-react-jsx has a pragma jsx, letting you to change JSX compilation rules. Preact, for example, configure it to produce just h.
• pragma jsx + webpack conf - the same, but webpack plugin will inject right imports.
• babel-plugin-transform-react-constant-elements would hoist Elements creating, thus removes object property access, as long it would be called only once. Plus - would remove GC pressure due to the same "one time" element creation.
• react-local - is doing absolutely the same, but as a babel plugin. Requires more work for proper instalation.
• runtime-compress-loader - compress all inlined babel helpers. The same action, but for js sugar.

Licence

MIT