@babel/preset-flow

This preset is recommended if you use Flow, a static type checker for JavaScript code. It includes the following plugins:

Example

In

  1. function foo(one: any, two: number, three?): string {}

Out

  1. function foo(one, two, three) {}

Installation

  1. npm install --save-dev @babel/preset-flow

Usage

With a configuration file (Recommended)

  1. {
  2.   "presets": ["@babel/preset-flow"]
  3. }

Via CLI

  1. babel --presets @babel/preset-flow script.js

Via Node API

  1. require("@babel/core").transform("code", {
  2.   presets: ["@babel/preset-flow"],
  3. });

Options

all

boolean, defaults to false.

Flow will only parse Flow-specific features if a @flow pragma is present atop the file, or the all option is set inside the .flowconfig.

If you are using the all option in your Flow config, be sure to set this option to true to get matching behavior.

For example, without either of the above set, the following call expression with a type argument:

  1. f<T>(e)

Would get parsed as a nested binary expression:

  1. f < T > e;

allowDeclareFields

boolean, defaults to false

NOTE: This will be enabled by default in Babel 8

When enabled, type-only class fields are only removed if they are prefixed with the declare modifier:

  1. class A {
  2.   declare foo: string; // Removed
  3.   bar: string; // Initialized to undefined
  4. }

You can read more about configuring preset options here