flow-remove-types


Turn your JavaScript with Flow type annotations into
standard JavaScript in an instant with no configuration and minimal setup.

Flow provides static type checking to JavaScript which
can both help find and detect bugs long before code is deployed and can make
code easier to read and more self-documenting. The Flow tool itself only reads
and analyzes code. Running code with Flow type annotations requires first
removing the annotations which are non-standard JavaScript. Typically this is
done via adding a plugin to your Babel configuration,
however Babel may be overkill if you're only targeting modern versions of
Node.js or just not using the modern ES2015 features that may not be in
every browser.

flow-remove-types is a faster, simpler, zero-configuration alternative with
minimal dependencies for super-fast npm install time.

Getting Started

Use the command line:

``bash
npm install --global flow-remove-types
`

`bash
flow-remove-types --help
flow-remove-types input.js > output.js
`

Or the JavaScript API:

`bash
npm install flow-remove-types
`

`js
var flowRemoveTypes = require('flow-remove-types');
var fs = require('fs');

var input = fs.readFileSync('input.js', 'utf8');
var output = flowRemoveTypes(input);
fs.writeFileSync('output.js', output.toString());
`

When using the flow-remove-types script, be sure not to direct the output to itself!

Use in Build Systems

Rollup: rollup-plugin-flow

Browserify: unflowify

Webpack: remove-flow-types-loader

Gulp: gulp-flow-remove-types

Use with existing development tools

* ESLint: eslint-plugin-flowtype
* Mocha: mocha -r flow-remove-types/register
* Jest: Add to your config:

`js
transform: {
"^.+\\.js(?:\\.flow)?$": "flow-remove-types/jest"
}
`

Use flow-node

Wherever you use node you can substitute flow-node and have a super fast
flow-types aware evaluator or REPL.

`bash
$ flow-node
> var x: number = 42
undefined
> x
42
`

> Note: This package is also available under the alias flow-node since it's
> often looked for at that location due to the popularity of this script. Both
> scripts are available no matter which package you install.

Use the require hook

Using the require hook allows you to automatically compile files on the fly when
requiring in node, useful during development:

`js
require('flow-remove-types/register')
require('./some-module-with-flow-type-syntax')
`

You can also provide options to the require hook:

`js
// Transforms all files, not just those with a "@flow" comment.
require('flow-remove-types/register')({ all: true })
`

Use options to define exactly which files to includes or excludes with regular
expressions. All files are included by default except those found in the
node_modules folder, which is excluded by default.

`js
require('flow-remove-types/register')({ includes: /\/custom_path\// })
`

> Don't use the require hook in packages distributed on NPM
> As always, don't forget to use flow-remove-types to compile files before distributing
> your code on npm, as using the require hook affects the whole runtime and not
> just your module and may hurt the runtime performance of code that includes it.

Dead-Simple Transforms

When flow-remove-types removes Flow types, it replaces them with whitespace.
This ensures that the transformed output has exactly the same number of lines
and characters and that all character offsets remain the same. This removes the
need for sourcemaps, maintains legible output, and ensures that it is super easy
to include flow-remove-types at any point in your existing build tools.

Built atop the official Flow parser,
flow-remove-types is designed to operate on the same syntax Flow itself understands.
It also passes through other common non-standard syntax such as JSX
and experimental ECMAScript proposals that Flow supports.

Before:

`js
import SomeClass from 'some-module'
import type { SomeInterface } from 'some-module'

export class MyClass extends SomeClass implements SomeInterface {

value: T

constructor(value: T) {
this.value = value
}

get(): T {
return this.value
}

}

`

After:

`js
import SomeClass from 'some-module'


export class MyClass extends SomeClass {

constructor(value ) {
this.value = value
}

get() {
return this.value
}

}
`

$3

Rather not have the whitespace? Pass the --pretty flag to remove the whitespace.

`bash
flow-remove-types --pretty --sourcemaps source.js
`

Or using the JS API:

`js
var flowRemoveTypes = require('flow-remove-types');
var fs = require('fs');

var input = fs.readFileSync('input.js', 'utf8');
var output = flowRemoveTypes(input, { pretty: true });
fs.writeFileSync('output.js', output.toString());
var sourceMap = output.generateMap();
fs.writeFileSync('output.js.map', JSON.stringify(sourceMap));
`

Performance

> NOTE: These timings are for flow-remove-types v1.

$3

Installing via npm from an empty project:

flow-remove-types:

`bash
time npm install flow-remove-types

real 0m3.193s
user 0m1.643s
sys 0m0.775s
`

Babel:

`bash
time npm install babel-cli babel-plugin-transform-flow-strip-types

real 0m23.200s
user 0m10.395s
sys 0m4.238s
`

$3

Transforming a directory of 20 files of 100 lines each:

flow-remove-types:

`bash
time flow-remove-types src/ --out-dir dest/

real 0m0.431s
user 0m0.436s
sys 0m0.068s
`

Babel:

`bash
time babel src/ --out-dir dest/

real 0m1.074s
user 0m1.092s
sys 0m0.149s
``