babel-plugin-const-enum

babel-plugin-const-enum ·

Transform TypeScript const enums

Install

Using npm:

npm install --save-dev babel-plugin-const-enum

or using yarn:

yarn add babel-plugin-const-enum --dev

Usage

You are most likely using @babel/preset-typescript or @babel/plugin-transform-typescript along with this plugin.

If you are using @babel/preset-typescript, then nothing special needs to be done since plugins run before presets.

If you are using @babel/plugin-transform-typescript, then make sure that babel-plugin-const-enum comes before @babel/plugin-transform-typescript in the plugin array so that babel-plugin-const-enum runs first. This plugin needs to run first to transform the const enums into code that @babel/plugin-transform-typescript allows.

.babelrc

{
  "plugins": ["const-enum", "@babel/transform-typescript"]
}

transform: removeConst (default)

Removes the const keyword to use regular enum. Can be used in a slower dev build to allow const, while prod still uses tsc. See babel#6476.

// Before:
const enum MyEnum {
  A = 1,
  B = A,
  C,
  D = C,
  E = 1,
  F,
  G = A * E,
  H = A ** B ** C,
  I = A << 20
}

// After:
enum MyEnum {
  A = 1,
  B = A,
  C,
  D = C,
  E = 1,
  F,
  G = A * E,
  H = A ** B ** C,
  I = A << 20
}

.babelrc

{
  "plugins": [
    "const-enum"
  ]
}

Or Explicitly:

.babelrc

{
  "plugins": [
    [
      "const-enum",
      {
        "transform": "removeConst"
      }
    ]
  ]
}

transform: constObject

Transforms into a const object literal. Can be further compressed using Uglify/Terser to inline enum access. See babel#8741.

// Before:
const enum MyEnum {
  A = 1,
  B = A,
  C,
  D = C,
  E = 1,
  F,
  G = A * E,
  H = A ** B ** C,
  I = A << 20
}

// After:
const MyEnum = {
  A: 1,
  B: 1,
  C: 2,
  D: 2,
  E: 1,
  F: 2,
  G: 1,
  H: 1,
  I: 1048576
};

.babelrc

{
  "plugins": [
    [
      "const-enum",
      {
        "transform": "constObject"
      }
    ]
  ]
}

Troubleshooting

SyntaxError

You may be getting a SyntaxError because you are running this plugin on non-TypeScript source. You might have run into this problem in react-native, see:
babel-plugin-const-enum#2
babel-plugin-const-enum#3

This seems to be caused by react-native transpiling flow code in node_modules. To fix this issue, please use babel-preset-const-enum to only run babel-plugin-const-enum on TypeScript files. If you wish to fix the issue manually, check out the solution in babel-plugin-const-enum#2.