JarCastingflow-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 targetting 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.
Get Started!
Use the command line:
npm install --global flow-remove-types
flow-remove-types --help
flow-remove-types input.js > output.js
Or the JavaScript API:
npm install flow-remove-types
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
Use flow-node
Wherever you use node you can substitute flow-node and have a super fast flow-types aware evaluator or REPL.
$ flow-node
> var x: number = 42
undefined
> x
42
Note: This package is also available under the alias
flow-nodesince 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:
require('flow-remove-types/register')
require('./some-module-with-flow-type-syntax')
You can also provide options to the require hook:
// 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.
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-typesto 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 excellent babylon parser, flow-remove-types shares the same parse rules as the source of truth as Flow Babel plugins. It also passes through other common non-standard syntax such as JSX and experimental ECMAScript proposals.
Before:
import SomeClass from 'some-module'
import type { SomeInterface } from 'some-module'
export class MyClass<T> extends SomeClass implements SomeInterface {
value: T
constructor(value: T) {
this.value = value
}
get(): T {
return this.value
}
}
After:
import SomeClass from 'some-module'
export class MyClass extends SomeClass {
constructor(value ) {
this.value = value
}
get() {
return this.value
}
}
Pretty Transform
Rather not have the whitespace? Pass the --pretty flag to remove the whitespace.
flow-remove-types --pretty --sourcemaps source.js
Or using the JS API:
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
Install:
Installing via npm from an empty project:
flow-remove-types:
time npm install flow-remove-types
real 0m3.193s
user 0m1.643s
sys 0m0.775s
Babel:
time npm install babel-cli babel-plugin-transform-flow-strip-types
real 0m23.200s
user 0m10.395s
sys 0m4.238s
Transform:
Transforming a directory of 20 files of 100 lines each:
flow-remove-types:
time flow-remove-types src/ --out-dir dest/
real 0m0.431s
user 0m0.436s
sys 0m0.068s
Babel:
time babel src/ --out-dir dest/
real 0m1.074s
user 0m1.092s
sys 0m0.149s
