babel-preset-const-enum

> Babel preset for TypeScript const enums

Install

Using npm:

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

or using yarn:

`sh
yarn add babel-preset-const-enum --dev
`

Description

This preset runs
babel-plugin-const-enum
only on files with extensions .ts or .tsx. This prevents SyntaxErrors from
happening when mistakenly running babel-plugin-const-enum on non-TypeScript
files such as flow, which uses a .js extension.

A babel preset is required because plugins don't have access to the file
extension of the file the plugin may run on.

Usage

You are most likely using
@babel/preset-typescript
as along with this preset. Make sure that babel-preset-const-enum comes after
@babel/preset-typescript in the preset array so that
babel-preset-const-enum runs first.
This preset needs to run first to transform the const enums into code that
@babel/preset-typescript allows.

.babelrc

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

$3

boolean, defaults to false.

Indicates that every file extension should be parsed.

$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
{
"presets": ["const-enum"]
}
`

Or Explicitly:

.babelrc

`json
{
"presets": [
[
"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
{
"presets": [
[
"const-enum",
{
"transform": "constObject"
}
]
]
}
``