Putout

Perfection is finally attained not when there is no longer anything to add, but when there is no longer anything to take away.

(c) Antoine de Saint Exupéry

🐊Putout is a JavaScript Linter, pluggable and configurable code transformer, drop-in ESLint replacement with built-in code printer and ability to fix syntax errors. It has a lot of transformations that keeps your codebase in a clean state, removing any code smell and making code readable according to best practices.

The main target is JavaScript, but:

• ✅ JSX;
• ✅ TypeScript;
• ✅ Yaml;
• ✅ Markdown;
• ✅ JSON;
• ✅ Ignore;

are also supported. Here is how it looks like:

Check out couple variants of plugins that does the same: linting debugger statement:

• ❌ SWCLint no-debugger: 49 lines;
• ❌ RSLint no-debugger: 48 lines;
• ❌ ESLint no-debugger: 43 lines;
• ❌ Rome no-debugger: 28 lines;
• ✅ 🐊Putout remove-debugger: 7 lines:

'use strict';

module.exports.report = () => 'Unexpected "debugger" statement';

module.exports.replace = () => ({
    debugger: '',
});

Choose wisely, competitors cannot even fix… 🤫

If I have seen further, it is by standing upon the shoulders of giants.

(c) Isaak Newton

• 💪 ESLint for stable releases and future proof API.
• 💪 Babel for amazing API documented in Handbook and responsiveness of a team.
• 💪 Prettier for minimalistic options and uniform codestyle.
• 💪 jscodeshift for making codemods simple and popular.

• ❌ ESLint avoids fixes that could change the runtime behavior.
• ❌ Babel produces throw-away code.
• ❌ Prettier is a formatter.
• ❌ jscodeshift has no config and plugins support.

☝️ 🐊Putout on the other hand can make more drastic code transformations that directly affects your codebase making it a better place to code 💻.

It can:

• ✅ remove unused variables;
• ✅ remove unused for-of variables;
• ✅ remove unused typescripts types;
• ✅ remove unreferenced variables;
• ✅ remove unused private fields;
• ✅ remove unused expressions;
• ✅ remove useless variables;
• ✅ remove useless Object.assign();
• ✅ remove useless replace();
• ✅ remove useless map;
• ✅ remove useless mapped types;
• ✅ remove useless mapping modifiers;
• ✅ remove useless continue;
• ✅ remove useless operand;
• ✅ remove useless array constructor;
• ✅ remove useless conditions;
• ✅ remove useless type conversion;
• ✅ remove useless functions;
• ✅ remove useless Array.from;
• ✅ remove useless spread;
• ✅ remove useless arguments;
• ✅ remove useless escape;
• ✅ remove useless async;
• ✅ remove useless await;
• ✅ remove useless typeof;
• ✅ remove useless template expressions;
• ✅ remove useless for-of;
• ✅ remove useless array.entries();
• ✅ remove debugger statement;
• ✅ remove iife;
• ✅ remove nested blocks;
• ✅ remove process.exit call;
• ✅ remove console.log calls;
• ✅ remove empty block statements;
• ✅ remove empty patterns;
• ✅ remove strict mode directive from esm;
• ✅ remove constant conditions;
• ✅ remove boolean from assertion;
• ✅ remove boolean from logical expressions;
• ✅ remove duplicates from TypeScript Union;
• ✅ remove unreachable code;
• ✅ remove duplicate keys;
• ✅ remove useless typescripts types;
• ✅ remove duplicate typescripts interface keys;
• ✅ replace test.only to test calls;
• ✅ replace test.skip to test calls;
• ✅ reuse duplicate init;
• ✅ split variable declarations;
• ✅ split nested destructuring;
• ✅ simplify assignment;
• ✅ simplify ternary;
• ✅ simplify logical expressions;
• ✅ if absent strict mode directive in commonjs add it;
• ✅ convert const to let (when needed to avoid TypeError);
• ✅ convert apply to spread;
• ✅ convert bitwise to logical operator;
• ✅ convert concat to flat;
• ✅ convert esm to commonjs (enabled for *.cjs);
• ✅ convert commonjs to esm (enabled for *.mjs);
• ✅ convert template with one expression to string;
• ✅ convert equal to strict equal;
• ✅ convert indexOf to includes;
• ✅ convert replace to replaceAll;
• ✅ convert assignment to arrow function;
• ✅ convert forEach to for...of;
• ✅ convert map to for...of;
• ✅ convert reduce to for...of;
• ✅ convert Math.sqrt() to Math.hypot();
• ✅ extract sequence expressions;
• ✅ extract object properties;
• ✅ add return await;
• ✅ remove useless Promise.resolve;
• ✅ convert Promise.reject to throw;
• ✅ declare before reference;
• ✅ declare undefined variables;
• ✅ declare imports first;
• ✅ apply as type assertions;
• ✅ apply utility types;
• ✅ apply array.at;
• ✅ apply filter(Boolean);
• ✅ apply isArray;
• ✅ apply if condition;
• ✅ apply await import;
• ✅ apply comparison order;
• ✅ apply flatMap();
• ✅ apply template literals;
• ✅ merge duplicate imports;
• ✅ merge duplicate functions;

npm i putout -D

Usage: putout [options] [path]
Options:
   -h, --help                  display this help and exit
   -v, --version               output version information and exit
   -f, --format [formatter]    use a specific output format, the default is: 'progress-bar' locally and 'dump' on CI
   -s, --staged                add staged files when in git repository
   -i, --interactive           set lint options using interactive menu
   --fix                       apply fixes of errors to code
   --fix-count [count = 10]    count of fixes rounds
   --rulesdir                  use additional rules from directory
   --transform [replacer]      apply Replacer, for example 'var __a = __b -> const __a = __b', read about Replacer https://git.io/JqcMn
   --plugins [plugins]         a comma-separated list of plugins to use
   --enable [rule]             enable the rule and save it to '.putout.json' walking up parent directories
   --disable [rule]            disable the rule and save it to '.putout.json' walking up parent directories
   --enable-all                enable all found rules and save them to '.putout.json' walking up parent directories
   --disable-all               disable all found rules (set baseline) and save them to '.putout.json' walking up parent directories
   --match [pattern]           read '.putout.json' and convert 'rules' to 'match' according to 'pattern'
   --fresh                     generate a fresh cache
   --no-config                 avoid reading '.putout.json'
   --no-ci                     disable the CI detection
   --no-cache                  disable the cache
   --no-worker                 disable worker thread

To find errors:

putout lib test

To fix errors:

putout lib test --fix

By default 🐊Putout uses all enabled by default plugins, anyways it can be run with a couple mentioned plugins (split with ","):

putout lib --plugins remove-debugger,remove-unused-variables

🐊Putout supports next environment variables:

• PUTOUT_FILES - files that should be processed by putout, divided by ",";
• PUTOUT_CONFIG_FILE - path to 🐊Putout config file;
• ESLINT_CONFIG_FILE - path to ESLint config file;
• NO_ESLINT - do not run ESLint after 🐊Putout;
• NO_ESLINT_WARNINGS - do not show ESLint warnings;

PUTOUT_FILES=lib,test putout --fix

To configure create .putout.json file and override any of default options.

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"]
}

🐊Putout supports two types of plugins, prefix with:

• ✅ @putout/plugin-;
• ✅ putout-plugin-;

To use your plugin createnpm package with keywords putout, putout-plugin and add it to .putout.json.

For example if you need to remove-something create 🐊Putout plugin with name putout-plugin-remove-something and it to package.json:

{
    "plugins": ["remove-something"]
}

🐊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 examples of work.

All examples works both in ESM and CommonJS.

CommonJS:

const putout = require('putout');

ESM:

import {putout} from 'putout';

import {putout} from 'putout';

const source = `
    const t = 'hello';
    const m = t + '!';
    console.log(t);
`;

putout(source, {
    plugins: ['remove-unused-variables'],
});

// returns
`
const t = 'hello';
console.log(t);
`;

import {putoutAsync} from 'putout';

const source = `
    const t = 'hello';
    const m = t + '!';
    console.log(t);
`;

await putoutAsync(source, {
    plugins: ['remove-unused-variables'],
});

// returns
`
const t = 'hello';
console.log(t);
`;

MIT