babel-plugin-const-enum ·  

> Transform TypeScript const enums

Install

Using npm:

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

or using yarn:

`sh
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

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

$3

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.

`ts
// 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
`json
{
"plugins": [
"const-enum"
]
}
`

Or Explicitly:

.babelrc
`json
{
"plugins": [
[
"const-enum",
{
"transform": "removeConst"
}
]
]
}
`

$3

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

`ts
// 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
`json
{
"plugins": [
[
"const-enum",
{
"transform": "constObject"
}
]
]
}
`

Troubleshooting

$3

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.