Putout is a pluggable and configurable code transformer with built-in eslint
, babel plugins
and jscodeshift codemods
support for js
, jsx
typescript
and flow
files. It has a lot of transforms that will keep your codebase in a clean state transforming any code smell
to readable code according to best practices.
- because eslint avoids fixes that could change the runtime behavior.
- because babel produces throw-away code;
- because prettier it is a formatter;
- because jscodeshift has no
config
andplugins
support.
The main difference of putout
is saving code transformation results directly in a source code in a day-to-day baisis.
npm i putout
Usage: putout [options] [path]
Options:
-h, --help display this help and exit
-v, --version output version information and exit
-f, --format use a specific output format - default: dump
-s, --staged add staged files when in git repository
--fix aply found fixes of errors to code
--fix-count count of fixes rounds (defaults to 10)
--rulesdir specify custom rulesdir
--enable enable rule by name in .putout.json
--disable disable rule by name in .putout.json
--enable-all enable all rules in .putout.json
--disable-all disable all rules in .putout.json
--ext specify JavaScript file extensions
--jsx enable jsx (default)
--flow enable flow
--cache enable .putoutcache to speed up processing
--update-cache enable .putoutcache to speed up processing from scratch
--remove-cache remove .putoutcache
--no-jsx disable jsx
--no-flow disable flow (default)
To find possible transform places:
putout lib test
To apply transforms:
putout lib test --fix
Putout
consists of a couple simple parts, here is workflow representation.
Putout
supports next environment variables
:
PUTOUT_FILES
- files that should be processed by putout, divided by ",";
PUTOUT_FILES=lib,test putout --fix
remove unused variables
function show() {
- const message = 'hello';
console.log('hello world');
}
remove unused private fields
class Hello {
#a = 5;
- #b = 3;
get() {
return this.#a;
};
}
remove unused expressions
function show(error) {
- showError;
}
remove useless variables
- function hi(a) {
- const b = a;
};
+ function hi(b) {
};
remove useless typeof
- typeof typeof 'hello';
+ typeof 'hello';
remove useless await
- await await Promise.resolve('hello');
+ await Promise.resolve('hello');
remove useless async
-const show = async () => {
+const show = () => {
console.log('hello');
};
remove useless arguments
onIfStatement({
push,
- generate,
- abc,
})
function onIfStatement({push}) {
}
convert templates
with one expression
to string>
-const c = `${a + b}`;
+const c = String(a + b);
remove useless escape
-const t = 'hello \"world\"';
-const s1 = `hello \"world\"`;
-const s = `hello \'world\'`;
+const t = 'hello "world"';
+const s1 = `hello "world"`;
+const s = `hello 'world'`;
remove useless Array.from
-for (const x of Array.from(y)) {}
+for (const x of y) {}
remove useless spread
-for (const x of [...y]) {}
+for (const x of y) {}
remove useless Promise.resolve
async () => {
- return Promise.resolve('x');
+ return 'x';
}
convertPromise.reject
to throw
async () => {
- return Promise.reject('x');
+ throw 'x';
}
remove debugger
statement
- debugger;
remove boolean
from logical expressions
-const t = true && false;
+const t = false;
remove nested blocks
for (const x of Object.keys(a)) {
- {
- console.log(x);
- }
+ console.log(x);
}
remove double negations
--if (!!a)
++if (a)
console.log('hi');
remove unreachable code
function hi() {
return 5;
- console.log('hello');
}
replace test.only
with test
calls
-test.only('some test here', (t) => {
+test('some test here', (t) => {
t.end();
});
replace test.skip
with test
calls
-test.skip('some test here', (t) => {
+test('some test here', (t) => {
t.end();
});
remove process.exit
call
-process.exit();
split variable declarations
-let a, b;
+let a;
+let b;
split nested destructuring
-const {a: {b}} = c;
+const {a} = c;
+const {b} = a;
simplify ternary
-module.exports = fs.copyFileSync ? fs.copyFileSync : copyFileSync;
+module.exports = fs.copyFileSync || copyFileSync;
remove console.log
calls
-console.log('hello');
remove empty block statements
-if (x > 0) {
-}
remove empty patterns
-const {} = process;
remove strict mode directive from esm
-'use strict';
-
import * from fs;
Add strict mode
directive in commonjs
if absent
+'use strict';
+
const fs = require('fs');
remove constant conditions
function hi(a) {
- if (2 < 3) {
- console.log('hello');
- console.log('world');
- }
+ console.log('hello');
+ console.log('world');
};
function world(a) {
- if (false) {
- console.log('hello');
- console.log('world');
- }
};
convert esm
to commonjs
(disabled)
-import hello from 'world';
+const hello = require('world');
convert commonjs
to esm
(disabled)
-const hello = require('world');
+import hello from 'world';
apply destructuring
-const hello = world.hello;
-const a = b[0];
+const {hello} = world;
+const [a] = b;
apply top-level-await (proposal-top-level-await, disabled)
import fs from 'fs';
-(async () => {
- const data = await fs.promises.readFile('hello.txt');
-})();
+const data = await fs.promises.readFile('hello.txt');
convert throw
statement into expression (proposal-throw-expressions, disabled)
-const fn = (a) => {throw Error(a);}
+const fn = (a) => throw Error(a);
apply optional chaining (proposal-optional-chaining, disabled)
-const result = hello && hello.world;
+const result = hello?.world;
nullish coalescing (proposal-nullish-coalescing, disabled)
-result = typeof result === 'undefined' ? 'hello': result;
result = result ?? 'hello';
apply shorthand properties
-export const setSession = (session) => ({
- payload: session,
+export const setSession = (payload) => ({
+ payload,
});
merge destructuring properties
-const {one} = require('numbers'):
-const {two} = require('numbers');
+ const {
+ one,
+ two
+} = require('numbers');
merge if
statements
-if (a > b)
- if (b < c)
- console.log('hi');
+if (a > b && b < c)
+ console.log('hi');
convert Math.pow
to exponentiation operator
-Math.pow(2, 4);
+2 ** 4;
convert anonymous
to arrow function
-module.exports = function(a, b) {
+module.exports = (a, b) => {
}
convert for
to for-of
-for (let i = 0; i < items.length; i++) {
+for (const item of items) {
-const item = items[i];
log(item);
}
convert forEach
to for-of
-Object.keys(json).forEach((name) => {
+for (const name of Object.keys(json)) {
manage(name, json[name]);
-});
+}
convert for-in
to for-of
-for (const name in object) {
- if (object.hasOwnProperty(name)) {
+for (const name of Object.keys(object)) {
console.log(a);
- }
}
-Object.keys(json).forEach((name) => {
manage(name, json[name]);
-});
+}
convert spread
to Array.from
-const places = [
...runPlugins(),
];
+const places = Array.from(runPlugins());
extract sequence expressions
-module.exports.x = 1,
-module.exports.y = 2;
+module.exports.x = 1;
+module.exports.y = 2;
extract object properties into variable
-const {replace} = putout.operator;
-const {isIdentifier} = putout.types;
+const {operator, types} = putout;
+const {replace} = operator;
+const {isIdentifier} = types;
convert apply
to spread
-console.log.apply(console, arguments);
+console.log(...arguments);
convert arguments
to rest
-function hello() {
- console.log(arguments);
+function hello(...args) {
+ console.log(args);
}
convert Object.assign
to merge spread
function merge(a) {
- return Object.assign({}, a, {
- hello: 'world'
- });
+ return {
+ ...a,
+ hello: 'world'
+ };
};
convert binary expression
to boolean
- const a = b === b;
+ const a = true;
convert top-level return
into process.exit()
(because EcmaScript Modules doesn't support top level return)
- return;
+ process.exit();
add await
to return promise()
statements (because it's faster, produces call stack and more readable)
async run () {
- return promise();
+ return await promise();
}
The putout
repo is comprised of many npm packages. It is a lerna monorepo similar to babel.
putout
use formatters similar to eslint's formatters.
You can specify a formatter using the --format
or -f
flag on the command line. For example, --format codeframe
uses the codeframe
formatter.
The built-in formatter options are:
dump
stream
json
codeframe
progress
Package | Version | Dependencies |
---|---|---|
@putout/formatter-dump |
||
@putout/formatter-stream |
||
@putout/formatter-progress |
||
@putout/formatter-json |
||
@putout/formatter-codeframe |
||
@putout/formatter-eslint |
Formatter function executes on every processed file, it should return output string
.
module.exports = ({name, source, places, index, count, filesCount, errorsCount}) => {
return '';
};
Here is list of options:
name
- name of processed filesource
- source code of processed fileindex
- current indexcount
- processing files countfilesCount
- count of files with errorserrorsCount
count of errors
You can avoid any of this and use only what you nead. To make possible using with putout
add prefix putout-formatter-
to your npm package
,
and add tags putput
, formatter
, putout-formatter
.
eslint formatters
can be used as well with help of @putout/formatter-eslint
this way:
Install:
npm i putout @putout/formatter-eslint eslint-formatter-pretty -D
Run:
ESLINT_FORMATTER=pretty putout -f eslint lib
To configure putout
add section putout
to your package.json
file or create .putout.json
file and override any of default options.
By default all rules located in plugins
section (and default rules) are enabled by default.
You can disable rules using "off", or enable them (in match
section) using "on".
{
"rules": {
"remove-unused-variables": "off"
}
}
Or pass options using rules
section:
{
"rules": {
"remove-unused-variables": ["on", {
"exclude": "const global = __"
}]
}
}
With help of exclude
you can set code pattern to exclude for current rule.
Pass an array when you have a couple templates to exclude.
exclude
is cross-plugins function supported by core, when develop your plugin, please use other name
to keep users ability to customize all plugins in a way the need to.
When you need to match paths to rules you can use match
section for this purpose in .putout.json
:
{
"match": {
"server": {
"remove-process-exit": true
}
}
}
When you need to ignore some routes no metter what, you can use ignore
section in .putout.json
:
{
"ignore": [
"test/fixture"
]
}
There is two types of plugins supported by putout
, their names in npm started with prefix:
@putout/plugin-
for official pluginsputout-plugin-
for user plugins
Example
If you need to remove-something
create putout
plugin with a name putout-plugin-remove-something
and add it to .putout.json
:
{
"plugins": [
"remove-something"
]
}
Add putout
as a peerDependency
to your packages.json
.
Always add keywords putout
, putout-plugin
when publish putout plugin to npm
so others can easily find it.
Let's consider a couple plugin types, that can be used.
The simplest putout
plugin type, consits of 2 functions:
report(path)
- report error message toputout
cli;replace
- replacekey
template intovalue
template;
module.exports.report = () => 'use optional chaining';
module.exports.replace = () => ({
'__a && __a.__b': '__a?.__b',
});
This plugin will find and sugest to replace all occurences of code: object && object.property
into `object?.property'.
More powerful plugin type, when you need more control over traversing. It should contain next 2 functions:
report(path)
- report error message toputout
cli;fix(path)
- fixes paths usingplaces
array received usingfind
function;
and one or more of this:
filter(path)
- filter path, should returntrue
, orfalse
(don't use withtraverse
);include
- returns array of templates, or node names to include;exclude
- returns array of templates, or node names to exclude;
module.exports.report = () => 'use optional chaining';
module.exports.include = () => [
'debugger'
];
module.exports.fix = (path) => {
path.remove(path);
};
More information about supported plugin types you can find in @putout/engine-runner.
When you need, you can use @babel/types, template and generate. All of this can be get from putout
:
const {
types,
template,
generate,
} = require('putout');
Most information you can find in Babel Plugin Handbook is relevant to putout
plugins.
To understand how things works from the inside take a look at Super Tiny Compiler.
When you need to use replaceWith
, replaceWithMultiple
, or insertAfter
, please use operator
insted of path
-methods.
const {template, operator} = require('putout');
const {replaceWith} = operator;
const ast = template.ast(`
const str = 'hello';
`);
module.exports.fix = (path) => {
// wrong
path.replaceWith(ast);
// correct
replaceWith(path, ast);
}
This should be done to preserve loc
and comments
information, which is different in babel
and recast
. putout
will handle this case for you :),
just use methods of operator
.
When you work on a plugin
or codemod
please add rule putout
into .putout.json
:
{
"rules": {
"putout": true
}
}
@putout/plugin-putout will handle plugin-specific cases for you :).
Let's consider simplest possible plugin for removing debugger statements
@putout/plugin-remove-debugger:
// this is a message to show in putout cli
module.exports.report = () => 'Unexpected "debugger" statement';
// lets find all "debugger" statements and replace them with ""
module.exports.replace = () => {
'debugger': '',
};
Visitor
used in traverse function
can be code template as well. So when you need to find module.exports = <something>
, you
can use:
module.exports.traverse = ({push}) => {
return {
'module.exports = __'(path) {
push(path);
}
}
};
Where __
is a placeholder for anything.
Remember: template key should be valid JavaScript, or Type name like in previous example.
You can aslo use include
and/or exclude
insead of traverse
and filter
(more sophisticated example):
// should be always used include/or exclude, when traverse not used
module.exports.include = () => [
'debugger',
];
// optional
module.exports.exclude = () => [
'console.log'
];
// optional
module.exports.filter = (path) => {
// do some checks
return true;
}
There is predefined placeholders:
__
- any code;"__"
- any string literal;__
- any template string literal;
That was the simplest module to remove debugger
statements in your code. Let's look how to test it using @putout/test:
const removeDebugger = require('..');
const test = require('@putout/test')(__dirname, {
'remove-debugger': removeDebugger,
});
// this is how we test that messages is correct
test('remove debugger: report', (t) => {
t.reportCode('debugger', 'Unexpected "debugger" statement');
t.end();
});
// stetement should be removed so result is empty
test('remove debugger: transformCode', (t) => {
t.transformCode('debugger', '');
t.end();
});
As you see test runner it is little bit modifed tape. To see more sophisticated example look at @putout/remove-console.
You can add babel
to plugins
section of .putout.json
with babel/
prefix.
You can disable rule, or use match in a similar, way
Example
Let's add babel-plugin-transform-inline-consecutive-adds
to .putout.json
:
{
"plugins": [
"babel/transform-inline-consecutive-adds"
]
}
Then create a file and process it with help of babel plugin
.
coderaiser@cloudcmd:~$ cat > a.js
const t = [];
t.push(1);
t.push(2);
coderaiser@cloudcmd:~$ putout a.js -f codeframe
/home/coderaiser/a.js:4:0
2 | t.push(1);
3 | t.push(2);
> 4 |
| ^ transform inline consecutive adds
✖ 1 errors in 1 files
fixable with the `--fix` option
coderaiser@cloudcmd:~$ putout --fix a.js
coderaiser@cloudcmd:~$ cat a.js
const t = [1, 2];
Using putout
as a runner for babel
plugins
you can not only change file content, but also see what exactly will be changed. You can use your already written
babel
plugins
or reuse work in progress plugins made for babel
, but remember that putout
plugins
gave more accurate information about changing places, and works faster (no need to find infromation about changes in transformed file).
Here you can find babel plugins
which feets the most main purpose of putout
and adviced to use:
transform-inline-consecutive-adds
-const foo = {};
-foo.a = 42;
-foo.b = ["hi"];
-foo.c = bar();
-foo.d = "str";
+const foo = {
+ a: 42,
+ b: ["hi"],
+ c: bar(),
+ d: "str"
+};
-const bar = [];
-bar.push(1);
-bar.push(2);
+const bar = [1, 2];
Please send pull requests with babel plugins
which can be used as codemods, or simplify, fix, makes code more readable.
jscodeshift
codemods can be added to plugins
section of .putout.json
with prefix jscodeshift/
. This way:
Example
{
"plugins": [
"jscodeshift/async-await-codemod"
]
}
Here you can find jscodeshift codemods
which feets the most main purpose of putout
and adviced to use:
async-await-codemod
-function makeRequest() {
- return getJSON().then(data => {
- console.log(data);
- return 'done';
- });
+ async function makeRequest() {
+ const data = await getJSON();
+ console.log(data);
+ return 'done';
}
Please send pull requests with jscodeshift codemods
which can be used to simplify, fix or makes code more readable.
putout
supports codemodes
in the similar to plugins way, just create a directory ~/.putout
and put your plugins there. Here is example: convert-tape-to-supertape and this is example of work.
If you see that putout
brokes formatting of your code, use eslint plugin eslint-plugin-putout.
Install eslint-plugin-putout
with:
npm i eslint eslint-plugin-putout -D
Then create .eslintrc.json
:
{
"extends": [
"plugin:putout/recommended"
],
"plugins": [
"putout"
]
}
And use with putout
this way:
putout --fix lib
To set custom eslint config file
use ESLINT_CONFIG_FILE
env variable:
ESLINT_CONFIG_FILE=test.eslintrc.json putout --fix lib
You can even use only eslint
, because putout
bundled to eslint-plugin-putout
with:
eslint --fix lib
Will uses putout transformations for you :).
Putout
can be used as babel plugin.
Just create .babelrc
file with configuration you need.
{
"plugins": [
["putout", {
"rules": {
"remove-unused-variables": false
}
}]
]
}
const putout = require('putout');
const source = `
const t = 'hello';
const m = t + '!';
console.log(t);
`;
const result = putout(source, {
plugins: [
'remove-unused-variables',
]
});
// returns
`
const t = 'hello';
console.log(t);
`
MIT