eslint-plugin-pureness

Check the pureness of some files.

1. Install the plugin via npm install --save-dev eslint-plugin-pureness
2. Include "pureness" to the "plugins": [] array of your .eslintrc file.
3. Add the rule definition to the "rules": {} object. See rules below.

• v2.2.1

- Docs fixed.

• v2.2.0

- pureness/forbid-new recognizes params so far. - new syntax of forbid-new rule introduced.

• v2.1.2

- ESLint version bumped.

• v2.1.1

- import/require things are now case-insensitive. This version still works with ESLint v2.x.x but installation emits warnings.

• v2.1.0

- import { forbidden } from 'non_forbidden'; recognized; - "*" is recognized as object name wildcard.

• v2.0.1

- documentation updated; - publishing.

• v2.0.0

- .eslint-plugin-pureness-rc removed; config now resides in .eslintrc; - "pureness/pure" does not exist anymore, see rules below.

• v1.0.1

- an error was fixed in the "pureness/pure" analyzer; - new Ctor() is considered as impure code too.

• v1.0.0 The newborn.

- Plugin understands impure expressions like Date.now(); - Expression list is configurable.Each rule ha syntax "pureness/<rule-name>": [<level>, <...options>], where

• <rule-name> is one of described below,
• <level> is error level to raise ("warn", "error", or 1 and 2 according to legacy rules),
• <...options> is the sequence of objects describing rule-specific parameters. Every option must contain the masks field (String or String[]). It determines files the rule is run against. A mask is the part of the full file path. If you have, for instance,

`"pureness/forbid-new": ["error", { "masks": ["formatter", "helper"], ... }]`  
both `src/formatters/time.es` and `src/utils/time-helper.es` are verified but `src/views/clock.es` is skipped for this particular rule.

Mind following:

• by default, without defining correct masks, plugin rules won't work;
• masks are case-insensitive (Unix and Windows users should work fine together;
• "*" means force verifying all files.

"pureness/forbidden-expressions": ["error", <...options>]

Forbids certain expressions in given files. <...options> is the sequence objects of following structure:

• "masks" is String or String[]; determines which files to verify;
• "expressions" is String or String[], determines the list of forbidden calls, like "ObjectName.methodName". "*" is allowed as a wildcard for both ObjectName and methodName.

**`"expressions"`** are case-sensitive (according to general ECMA language principles).

Example:

// ----- single rule -----
"pureness/forbidden-expressions": ["error",
  {
    "masks": "formatter",
    "expressions": ["Date.now", "_.now"]
  }
]

// ----- different rules for different areas -----
"pureness/forbidden-expressions": ["error",
  {
    "masks": ["formatter", "helper"],
    "expressions": ["Date.now", "_.now"]
  },
  {
    "masks": "view",
    "expressions": ["adapter.*", "Math.random"]
  }
]

"pureness/forbidden-import": ["error", <...options>]

Forbids importing/requiring certain modules in given files. <...options> work in same way as in "pureness/forbidden-expressions" but use "modules" instead of "expressions".

• Part of the module name works as a mask so example below works against both require('./classMate') and require('classnames').
• "modules" are case-insensitive, so import Cls from './MyPrettyClass' also raises an error (see example).
• Submodules and import decomposition is also analyzed. import { MyClass } from './allowed-file' raises the error with the example as well.

Example:

"pureness/forbidden-import": ["error",
  {
    "masks": "formatter",
    "modules": ["adapter", "class"]
  }
]

"pureness/forbid-new": ["warn", <...options>]

Raises the error/warning when meets new AnyConstructor() in given files. <...options> is sequence of objects of following structure:

• "masks" is String or String[]; determines which files to verify;
• "allow" is String or String[]; determines list of constructors that are allowed.

For example, `new Promise()` does not affect code pureness;

• "allow-with-params" or "allowWithParams" is String or String[], determines the list of constructors that produce pure code being called with params.

For example, `new Date()` is impure because changes result from time to time; `new Date(2016, 12, 31)` always returns similar object (however not _the same_ object) so might be considered as pure.

The legacy (v2.1.x and below) syntax "pureness/forbid-new": ["warn", <...masks>] is still supported.
Example (legacy syntax): "pureness/forbid-new": ["warn", "formatter", "helper"]
Example (syntax of v2.2.x):

"pureness/forbid-new": ["warn",
  {
    "masks": ["formatter", "helper"],
    "allow-with-params": ["Date"]
  },
  {
    "masks": "views"
  },
  {
    "masks": "*",
    "allow": "Promise"
  }
]

1. Run npm install.

- Run npm install && npm install eslint (it's mandatory to install eslint separately because npm changed the peerDependencies treatment since v3).

1. Create the softlink from project root folder to node_modules\eslint-plugin-pureness:

- Linux: sudo ln -s $(pwd) $(pwd)/node_modules/eslint-plugin-pureness; - Windows: junction -s node_modules\eslint-plugin-pureness .\ (usually you have to install the junction).

1. Run node node_modules/eslint/bin/eslint.js test-me/* to check how the plugin works.
2. After development is done,

1. create new git annotated tag, git tag -a <version.number> -m "New release" 1. and push it: git push origin <version.number>
The EsLint.RuleTester will be introduced with one of next releases.

---

Roman Melnyk, , (https://codedoc255.wordpress.com)