生产环境优化

• 关于 react.js 和 react.min.js

前者用于开发, 包含额外的错误提示, 后者用上生产环境, 做了一些优化, 移除了错误提示

如果要在 webpack 打包出等价的 react.min.js

module.exports = {
  //...
  plugins:[
    new webpack.DefinePlugin({
      'process.env':{
        'NODE_ENV': JSON.stringify('production')
      }
    }),
    new webpack.optimize.UglifyJsPlugin({
      compress:{
        warnings: false
      }
    })
  ]
  //...
}

观察 react 源码里存在大量环境判断类似:

function cloneWithProps(child, props) {
  if (process.env.NODE_ENV !== 'production') {
    process.env.NODE_ENV !== 'production' ? warning(didDeprecatedWarn, 'cloneWithProps(...) is deprecated. ' + 'Please use React.cloneElement instead.') : undefined;
    didDeprecatedWarn = true;
    process.env.NODE_ENV !== 'production' ? warning(!child.ref, 'You are calling cloneWithProps() on a child with a ref. This is ' + 'dangerous because you\'re creating a new child which will not be ' + 'added as a ref to its parent.') : undefined;
  }

  var newProps = ReactPropTransferer.mergeProps(props, child.props);

  // Use `child.props.children` if it is provided.
  if (!newProps.hasOwnProperty(CHILDREN_PROP) && child.props.hasOwnProperty(CHILDREN_PROP)) {
    newProps.children = child.props.children;
  }

  // The current API doesn't retain _owner, which is why this
  // doesn't use ReactElement.cloneAndReplaceProps.
  return ReactElement.createElement(child.type, newProps);
}

这种分支判断属于空代码在压缩后会移除掉

The issue body explains React's development and production builds and shows a webpack configuration using DefinePlugin and UglifyJsPlugin. No repository file, test, or entry point is named; first clarify where this explanation belongs and what documentation change is expected. Done should be a clearly scoped, accurate note about removing development-only branches in the production build.