Ben Alpert ff8a10e52f Add option to block-scoping to slow on throw code (#5236 )

The let/const plugin can add closures where you don't expect them. This is undesirable in some perf-sensitive projects (ex: React). I added an option that throws whenever the plugin adds a function (as opposed to simply renaming variables when converting to var).

2017-02-06 13:50:56 -05:00

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babel-plugin-transform-es2015-block-scoping

Compile ES2015 block scoping (const and let) to ES5

Installation

npm install --save-dev babel-plugin-transform-es2015-block-scoping

Usage

Via `.babelrc` (Recommended)

.babelrc

Without options:

{
  "plugins": ["transform-es2015-block-scoping"]
}

With options:

{
  "plugins": [
    ["transform-es2015-block-scoping", {
      "throwIfClosureRequired": true
    }]
  ]
}

Via CLI

babel --plugins transform-es2015-block-scoping script.js

Via Node API

require("babel-core").transform("code", {
  plugins: ["transform-es2015-block-scoping"]
});

Options `throwIfClosureRequired`

In cases such as the following it's impossible to rewrite let/const without adding an additional function and closure while transforming:

for (let i = 0; i < 5; i++) {
  setTimeout(() => console.log(i), 1);
}

In extremely performance-sensitive code, this can be undesirable. If "throwIfClosureRequired": true is set, Babel throws when transforming these patterns instead of automatically adding an additional function.

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