├── .gitignore ├── package.json ├── index.js ├── README.md └── LICENSE /.gitignore: -------------------------------------------------------------------------------- 1 | # Logs 2 | logs 3 | *.log 4 | npm-debug.log* 5 | 6 | # Runtime data 7 | pids 8 | *.pid 9 | *.seed 10 | 11 | # Directory for instrumented libs generated by jscoverage/JSCover 12 | lib-cov 13 | 14 | # Coverage directory used by tools like istanbul 15 | coverage 16 | 17 | # Grunt intermediate storage (http://gruntjs.com/creating-plugins#storing-task-files) 18 | .grunt 19 | 20 | # node-waf configuration 21 | .lock-wscript 22 | 23 | # Compiled binary addons (http://nodejs.org/api/addons.html) 24 | build/Release 25 | 26 | # Dependency directory 27 | node_modules 28 | 29 | # Optional npm cache directory 30 | .npm 31 | 32 | # Optional REPL history 33 | .node_repl_history 34 | -------------------------------------------------------------------------------- /package.json: -------------------------------------------------------------------------------- 1 | { 2 | "name": "eslint-plugin-immutable", 3 | "version": "1.0.0", 4 | "description": "ESLint plugin to disable all mutation in JavaScript.", 5 | "main": "index.js", 6 | "scripts": { 7 | "test": "echo \"Error: no test specified\" && exit 1" 8 | }, 9 | "repository": { 10 | "type": "git", 11 | "url": "git+https://github.com/jhusain/eslint-plugin-immutable.git" 12 | }, 13 | "keywords": [ 14 | "eslint", 15 | "immutability" 16 | ], 17 | "author": "Jafar Husain", 18 | "license": "Apache-2.0", 19 | "bugs": { 20 | "url": "https://github.com/jhusain/eslint-plugin-immutable/issues" 21 | }, 22 | "homepage": "https://github.com/jhusain/eslint-plugin-immutable#readme" 23 | } 24 | -------------------------------------------------------------------------------- /index.js: -------------------------------------------------------------------------------- 1 | "use strict"; 2 | 3 | module.exports = { 4 | rules: { 5 | "no-let": function(context) { 6 | return { 7 | "VariableDeclaration": function(node) { 8 | if (node.kind === "let") { 9 | context.report(node, "Unexpected let, use const."); 10 | } 11 | } 12 | }; 13 | }, 14 | "no-this": function(context) { 15 | return { 16 | "ThisExpression": function(node) { 17 | context.report(node, "Unexpected this, use functions not classes."); 18 | } 19 | } 20 | }, 21 | "no-mutation": function(context) { 22 | return { 23 | "AssignmentExpression": function(node) { 24 | if (node.left.type === "MemberExpression") { 25 | context.report(node, "No object mutation allowed."); 26 | } 27 | } 28 | } 29 | } 30 | }, 31 | configs: { 32 | recommended: { 33 | rules: { 34 | 'redux/no-let': 2, 35 | 'redux/no-this': 2, 36 | 'redux/no-mutation': 2 37 | } 38 | } 39 | } 40 | }; 41 | 42 | 43 | //no-undef 44 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # eslint-plugin-immutable 2 | 3 | This is an ESLint plugin to disable all mutation in JavaScript. Think this is a bit too restrictive? Well if you're using Redux and React, there isn't much reason for your code to be mutating *anything*. Redux maintains a mutable pointer to your immutable application state, and React manages your DOM state. Your components should be stateless functions, translating data into Virtual DOM objects whenever Redux emits a new state. These ESLint rules explicitly prohibit mutation, effectively forcing you to write code very similar to [Elm](http://elm-lang.org/) in React. 4 | 5 | ## Installing 6 | 7 | `npm install eslint-plugin-immutable --save-dev` 8 | 9 | ## ESLint Rules 10 | There are three rules in the plugin: 11 | 12 | ### no-let 13 | 14 | There's no reason to use `let` in a Redux/React application, because all your state is managed by either Redux or React. Use `const` instead, and avoid state bugs altogether. 15 | 16 | ```JavaScript 17 | let x = 5; // <- Unexpected let or var, use const. 18 | ``` 19 | 20 | What about `for` loops? Loops can be replaced with the Array methods like `map`, `filter`, and so on. If you find the built-in JS Array methods lacking, use [lodash](https://github.com/lodash/lodash). 21 | 22 | ```JavaScript 23 | const SearchResults = 24 | ({ results }) => 25 | ; 28 | ``` 29 | 30 | ### no-this 31 | 32 | Thanks to libraries like [recompose](https://github.com/acdlite/recompose) and Redux's [React Container components](http://redux.js.org/docs/basics/UsageWithReact.html), there's not much reason to build Components using `React.createClass` or ES6 classes anymore. The `no-this` rule makes this explicit. 33 | 34 | ```JavaScript 35 | const Message = React.createClass({ 36 | render: function() { 37 | return
{ this.props.message }
; // <- no this allowed 38 | } 39 | }) 40 | ``` 41 | 42 | Instead of creating classes, you should use React 0.14's [Stateless Functional Components](https://medium.com/@joshblack/stateless-components-in-react-0-14-f9798f8b992d#.t5z2fdit6) and save yourself some keystrokes: 43 | 44 | ```JavaScript 45 | const Message = ({message}) =>
{ message }
; 46 | ``` 47 | 48 | What about lifecycle methods like `shouldComponentUpdate`? We can use the [recompose](https://github.com/acdlite/recompose) library to apply these optimizations to your Stateless Functional Components. The [recompose](https://github.com/acdlite/recompose) library relies on the fact that your Redux state is immutable to efficiently implement shouldComponentUpdate for you. 49 | 50 | ```JavaScript 51 | import { pure, onlyUpdateForKeys } from 'recompose'; 52 | 53 | const Message = ({message}) =>
{ message }
; 54 | 55 | // Optimized version of same component, using shallow comparison of props 56 | // Same effect as React's PureRenderMixin 57 | const OptimizedMessage = pure(Message); 58 | 59 | // Even more optimized: only updates if specific prop keys have changed 60 | const HyperOptimizedMessage = onlyUpdateForKeys(['message'], Message); 61 | ``` 62 | 63 | ### no-mutation 64 | 65 | You might think that prohibiting the use of `let` and `var` would eliminate mutation from your JavaScript code. **Wrong.** Turns out that there's a pretty big loophole in `const`... 66 | 67 | ```JavaScript 68 | const point = { x: 23, y: 44 }; 69 | point.x = 99; // This is legal 70 | ``` 71 | 72 | This is why the `no-mutation` rule exists. This rule prevents you from assigning a value to the result of a member expression. 73 | 74 | ```JavaScript 75 | const point = { x: 23, y: 44 }; 76 | point.x = 99; // <- No object mutation allowed. 77 | ``` 78 | 79 | This rule is just as effective as using Object.freeze() to prevent mutations in your Redux reducers. However this rule has **no run-time cost.** A good alternative to object mutation is to use the object spread syntax coming in ES2016. 80 | 81 | ```JavaScript 82 | const point = { x: 23, y: 44 }; 83 | const transformedPoint = { ...point, x: 99 }; 84 | ``` 85 | 86 | You can enable this syntax using the [syntax-object-rest-spread](https://babeljs.io/docs/plugins/syntax-object-rest-spread/) [Babel](https://babeljs.io/) plug-in. 87 | 88 | ## Supplementary ESLint Rules to Enable 89 | 90 | The rules in this package alone can not eliminate mutation in your JavaScript programs. To go the distance I suggest you also enable the following built-in ESLint rules: 91 | 92 | * no-var (self-explanatory) 93 | * no-undef (prevents assigning to global variables that haven't been declared) 94 | * no-param-reassign (prevents assigning to variables introduced as function parameters) 95 | 96 | ## Sample Configuration File 97 | 98 | Here's a sample ESLint configuration file that activates these rules: 99 | 100 | ``` 101 | { 102 | "extends": "airbnb", 103 | "plugins": [ 104 | "immutable" 105 | ], 106 | "rules": { 107 | "immutable/no-let": 2, 108 | "immutable/no-this": 2, 109 | "immutable/no-mutation": 2 110 | } 111 | } 112 | ``` 113 | 114 | Special Thanks to [cerealbox](https://github.com/cerealbox) who paired with me on this. 115 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. Definitions. 8 | 9 | "License" shall mean the terms and conditions for use, reproduction, 10 | and distribution as defined by Sections 1 through 9 of this document. 11 | 12 | "Licensor" shall mean the copyright owner or entity authorized by 13 | the copyright owner that is granting the License. 14 | 15 | "Legal Entity" shall mean the union of the acting entity and all 16 | other entities that control, are controlled by, or are under common 17 | control with that entity. For the purposes of this definition, 18 | "control" means (i) the power, direct or indirect, to cause the 19 | direction or management of such entity, whether by contract or 20 | otherwise, or (ii) ownership of fifty percent (50%) or more of the 21 | outstanding shares, or (iii) beneficial ownership of such entity. 22 | 23 | "You" (or "Your") shall mean an individual or Legal Entity 24 | exercising permissions granted by this License. 25 | 26 | "Source" form shall mean the preferred form for making modifications, 27 | including but not limited to software source code, documentation 28 | source, and configuration files. 29 | 30 | "Object" form shall mean any form resulting from mechanical 31 | transformation or translation of a Source form, including but 32 | not limited to compiled object code, generated documentation, 33 | and conversions to other media types. 34 | 35 | "Work" shall mean the work of authorship, whether in Source or 36 | Object form, made available under the License, as indicated by a 37 | copyright notice that is included in or attached to the work 38 | (an example is provided in the Appendix below). 39 | 40 | "Derivative Works" shall mean any work, whether in Source or Object 41 | form, that is based on (or derived from) the Work and for which the 42 | editorial revisions, annotations, elaborations, or other modifications 43 | represent, as a whole, an original work of authorship. For the purposes 44 | of this License, Derivative Works shall not include works that remain 45 | separable from, or merely link (or bind by name) to the interfaces of, 46 | the Work and Derivative Works thereof. 47 | 48 | "Contribution" shall mean any work of authorship, including 49 | the original version of the Work and any modifications or additions 50 | to that Work or Derivative Works thereof, that is intentionally 51 | submitted to Licensor for inclusion in the Work by the copyright owner 52 | or by an individual or Legal Entity authorized to submit on behalf of 53 | the copyright owner. For the purposes of this definition, "submitted" 54 | means any form of electronic, verbal, or written communication sent 55 | to the Licensor or its representatives, including but not limited to 56 | communication on electronic mailing lists, source code control systems, 57 | and issue tracking systems that are managed by, or on behalf of, the 58 | Licensor for the purpose of discussing and improving the Work, but 59 | excluding communication that is conspicuously marked or otherwise 60 | designated in writing by the copyright owner as "Not a Contribution." 61 | 62 | "Contributor" shall mean Licensor and any individual or Legal Entity 63 | on behalf of whom a Contribution has been received by Licensor and 64 | subsequently incorporated within the Work. 65 | 66 | 2. Grant of Copyright License. Subject to the terms and conditions of 67 | this License, each Contributor hereby grants to You a perpetual, 68 | worldwide, non-exclusive, no-charge, royalty-free, irrevocable 69 | copyright license to reproduce, prepare Derivative Works of, 70 | publicly display, publicly perform, sublicense, and distribute the 71 | Work and such Derivative Works in Source or Object form. 72 | 73 | 3. Grant of Patent License. Subject to the terms and conditions of 74 | this License, each Contributor hereby grants to You a perpetual, 75 | worldwide, non-exclusive, no-charge, royalty-free, irrevocable 76 | (except as stated in this section) patent license to make, have made, 77 | use, offer to sell, sell, import, and otherwise transfer the Work, 78 | where such license applies only to those patent claims licensable 79 | by such Contributor that are necessarily infringed by their 80 | Contribution(s) alone or by combination of their Contribution(s) 81 | with the Work to which such Contribution(s) was submitted. If You 82 | institute patent litigation against any entity (including a 83 | cross-claim or counterclaim in a lawsuit) alleging that the Work 84 | or a Contribution incorporated within the Work constitutes direct 85 | or contributory patent infringement, then any patent licenses 86 | granted to You under this License for that Work shall terminate 87 | as of the date such litigation is filed. 88 | 89 | 4. Redistribution. You may reproduce and distribute copies of the 90 | Work or Derivative Works thereof in any medium, with or without 91 | modifications, and in Source or Object form, provided that You 92 | meet the following conditions: 93 | 94 | (a) You must give any other recipients of the Work or 95 | Derivative Works a copy of this License; and 96 | 97 | (b) You must cause any modified files to carry prominent notices 98 | stating that You changed the files; and 99 | 100 | (c) You must retain, in the Source form of any Derivative Works 101 | that You distribute, all copyright, patent, trademark, and 102 | attribution notices from the Source form of the Work, 103 | excluding those notices that do not pertain to any part of 104 | the Derivative Works; and 105 | 106 | (d) If the Work includes a "NOTICE" text file as part of its 107 | distribution, then any Derivative Works that You distribute must 108 | include a readable copy of the attribution notices contained 109 | within such NOTICE file, excluding those notices that do not 110 | pertain to any part of the Derivative Works, in at least one 111 | of the following places: within a NOTICE text file distributed 112 | as part of the Derivative Works; within the Source form or 113 | documentation, if provided along with the Derivative Works; or, 114 | within a display generated by the Derivative Works, if and 115 | wherever such third-party notices normally appear. The contents 116 | of the NOTICE file are for informational purposes only and 117 | do not modify the License. You may add Your own attribution 118 | notices within Derivative Works that You distribute, alongside 119 | or as an addendum to the NOTICE text from the Work, provided 120 | that such additional attribution notices cannot be construed 121 | as modifying the License. 122 | 123 | You may add Your own copyright statement to Your modifications and 124 | may provide additional or different license terms and conditions 125 | for use, reproduction, or distribution of Your modifications, or 126 | for any such Derivative Works as a whole, provided Your use, 127 | reproduction, and distribution of the Work otherwise complies with 128 | the conditions stated in this License. 129 | 130 | 5. Submission of Contributions. Unless You explicitly state otherwise, 131 | any Contribution intentionally submitted for inclusion in the Work 132 | by You to the Licensor shall be under the terms and conditions of 133 | this License, without any additional terms or conditions. 134 | Notwithstanding the above, nothing herein shall supersede or modify 135 | the terms of any separate license agreement you may have executed 136 | with Licensor regarding such Contributions. 137 | 138 | 6. Trademarks. This License does not grant permission to use the trade 139 | names, trademarks, service marks, or product names of the Licensor, 140 | except as required for reasonable and customary use in describing the 141 | origin of the Work and reproducing the content of the NOTICE file. 142 | 143 | 7. Disclaimer of Warranty. Unless required by applicable law or 144 | agreed to in writing, Licensor provides the Work (and each 145 | Contributor provides its Contributions) on an "AS IS" BASIS, 146 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 147 | implied, including, without limitation, any warranties or conditions 148 | of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A 149 | PARTICULAR PURPOSE. You are solely responsible for determining the 150 | appropriateness of using or redistributing the Work and assume any 151 | risks associated with Your exercise of permissions under this License. 152 | 153 | 8. Limitation of Liability. In no event and under no legal theory, 154 | whether in tort (including negligence), contract, or otherwise, 155 | unless required by applicable law (such as deliberate and grossly 156 | negligent acts) or agreed to in writing, shall any Contributor be 157 | liable to You for damages, including any direct, indirect, special, 158 | incidental, or consequential damages of any character arising as a 159 | result of this License or out of the use or inability to use the 160 | Work (including but not limited to damages for loss of goodwill, 161 | work stoppage, computer failure or malfunction, or any and all 162 | other commercial damages or losses), even if such Contributor 163 | has been advised of the possibility of such damages. 164 | 165 | 9. Accepting Warranty or Additional Liability. While redistributing 166 | the Work or Derivative Works thereof, You may choose to offer, 167 | and charge a fee for, acceptance of support, warranty, indemnity, 168 | or other liability obligations and/or rights consistent with this 169 | License. However, in accepting such obligations, You may act only 170 | on Your own behalf and on Your sole responsibility, not on behalf 171 | of any other Contributor, and only if You agree to indemnify, 172 | defend, and hold each Contributor harmless for any liability 173 | incurred by, or claims asserted against, such Contributor by reason 174 | of your accepting any such warranty or additional liability. 175 | 176 | END OF TERMS AND CONDITIONS 177 | 178 | APPENDIX: How to apply the Apache License to your work. 179 | 180 | To apply the Apache License to your work, attach the following 181 | boilerplate notice, with the fields enclosed by brackets "{}" 182 | replaced with your own identifying information. (Don't include 183 | the brackets!) The text should be enclosed in the appropriate 184 | comment syntax for the file format. We also recommend that a 185 | file or class name and description of purpose be included on the 186 | same "printed page" as the copyright notice for easier 187 | identification within third-party archives. 188 | 189 | Copyright {yyyy} {name of copyright owner} 190 | 191 | Licensed under the Apache License, Version 2.0 (the "License"); 192 | you may not use this file except in compliance with the License. 193 | You may obtain a copy of the License at 194 | 195 | http://www.apache.org/licenses/LICENSE-2.0 196 | 197 | Unless required by applicable law or agreed to in writing, software 198 | distributed under the License is distributed on an "AS IS" BASIS, 199 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 200 | See the License for the specific language governing permissions and 201 | limitations under the License. 202 | --------------------------------------------------------------------------------