ESLint Complexity of Code

ESLintCC is a ECMAScript/JavaScript/TypeScript tool that computes complexity of code by using ESLint

ESLint calculates complexity of code, while this tool only collects a report based on his complexity rule messages

Installation and Usage

Requirements, principles of local and global installation and usage are the same as ESLint Installation and Usage

Globally:

$ npm install -g eslintcc
$ eslintcc yourfile.js

Locally:

$ npm install eslintcc
$ ./node_modules/.bin/eslintcc yourfile.js

NPX (you can do it without installing):

$ npx eslintcc yourfile.js

Integration in JavaScript application (see more…):

const { Complexity } = require('eslintcc');

const complexity = new Complexity();
const report = await complexity.lintFiles(['yourfile.js']);

console.log(JSON.stringify(report, null, '\t'));

Note: ESLintCC ignores all rules, specified in configuration files, and uses to generate a report only complexity rules.

Configuration

ESLintCC uses ESLint along with Its configuration system. You can use configuration comments and files, as described in the configuration for ESLint.

Difference: ESLintCC uses its own settings for complexity rules, so they cannot be overridden through a configuration file. However, you can disable them locally in the file.

Features:

1. You can configurate parserOptions or parser for specify the JavaScript language support. .eslintrc.json:

{
  "parserOptions": {
    "ecmaVersion": 2021,
    "sourceType": "module"
  }
}

{
  "parser": "@typescript-eslint/parser"
}

1. You can disable checks for a specific complexity rule for a file or part of file using a comment:

// For a file
/* eslint max-params: off, max-depth: off */

function myFunc(a, b, c, d, e) {
  //...
}

// For a block
/* eslint-disable max-params */
function myFunc(a, b, c, d, e) {
  //...
}
/* eslint-enable max-params */
function myFunc2(a, b) {
  //...
}

// For a line
/* eslint-disable-next-line max-params */
function myFunc(a, b, c, d, e) {
  //...
}

Customize parser

Examples of ESLint Parser configuration

Babel parser

Using Babel you can support experimental syntax. For example private fields and methods for classes.

See package @babel/eslint-parser

package.json

{
  "devDependencies": {
    "@babel/eslint-parser": "latest",
    "@babel/plugin-proposal-class-properties": "latest",
    "@babel/plugin-proposal-private-methods": "latest"
  }
}

.eslintrc.json

{
  "parser": "@babel/eslint-parser",
  "parserOptions": {
    "sourceType": "module",
    "babelOptions": {
      "configFile": "./babel.config.json"
    }
  }
}

.babel.config.json

{
  "plugins": [
    "@babel/plugin-proposal-class-properties",
    "@babel/plugin-proposal-private-methods"
  ]
}

TypeScript parser

See package @typescript-eslint/parser

This parser is used you can add a code complexity score to your TypeScript project. In this case, the same standard ESLint rules are used for calculating complexity, described in “Complexity ranks” section.

package.json

{
  "devDependencies": {
    "typescript": "latest",
    "@typescript-eslint/parser": "latest",
    "@typescript-eslint/eslint-plugin": "latest"
  }
}

.eslintrc.json

{
  "overrides": [
    {
      "files": [
        "*.ts"
      ],
      "parser": "@typescript-eslint/parser",
      "plugins": [
        "@typescript-eslint"
      ],
      "extends": [
        "eslint:recommended",
        "plugin:@typescript-eslint/recommended"
      ]
    }
  ]
}

Complexity ranks

Every function and block will be ranked from A (best complexity score) to F (worst one). This ranks is based on the ranks of complexity of the Python Radon.

Rank Risk

• A low - simple block
• B low - well structured and stable block
• C moderate - slightly complex block
• D more than moderate - more complex block
• E high - complex block, alarming
• F very high - error-prone, unstable block

Ranks corresponds to rule complexity scores as follows:

Rules	A	B	C	D	E	F
Logic:
complexity	1 - 5	6 - 10	11 - 20	21 - 30	31 - 40	41 +
max-depth	1 - 2	3	4 - 5	6 - 7	8	9 +
max-nested-callbacks	1 - 3	4 - 5	6 - 10	11 - 15	16 - 20	21 +
max-params	1	2	3 - 4	5	6	7 +
Raw:
max-lines	1 - 75	76 - 150	151 - 300	301 - 450	451 - 600	601 +
max-lines-per-function	1 - 13	14 - 25	26 - 50	51 - 75	76 - 100	101 +
max-statements	1 - 3	4 - 5	6 - 10	11 - 15	16 - 20	21 +

Note: For rank “C”, the maximum score, using from the standard score of ESLint rules. See complexity rules. Other rules are calculated relative to the values of the “complexity” rule.

Example formula: [5, 10, 20, 30, 40].map(score => Math.round((score / 20) * defaultRuleScoreLimit))

Command line options

Command line format:

$ eslintcc [options] file.js [file.js] [dir]

Option	Type	Description
–rules <rules>, -r=<rules>	Array of String	Rule, or group: all, logic, raw. Default: logic
–format <format>, -f=<format>	String	Use a specific output format, text or json. Default: text
–average, -a	Flag	Show the average complexity at the end of output, if used text format
–show-rules, -sr	Flag	Show rule name and value, if used text format
–greater-than <value>, -gt=<value>	String or Number	Will show rules more than rank a, b, c, d, e, or rank value
–less-than <value>, -lt=<value>	String or Number	Will show rules less than rank b, c, d, e, f, or rank value
–no-inline-config, -nlc	Flag	Disable the use of configuration comments (such as /*eslint-disable*/)
–max-rank <value>, -mr=<value>	String or Number	Maximum allowed complexity rank for a single message. Default: C
–max-average-rank <value>, -mar=<value>	String or Number	Maximum allowed complexity rank for average value. Default: B

If the rank value for one message or the average value is higher than the allowed value, the program terminates with error code 1

Command examples

Output as JSON and show rules more than rank E:

$ npx eslintcc -f=json -gt=e file.js

Use only 2 rules and show rule name:

$ npx eslintcc --rules complexity --rules max-depth --show-rules file.js

Output examples

Based on the test files from the directory: ./test/src/

  $ npx eslintcc --show-rules ./test/src/complexity__max_rank.js
  B test/src/complexity__max_rank.js
    D  3:0 function MyFunc (max-params = 4)
    A  9:0 function MyFunc1 (max-params = 1)
    A 15:0 function MyFunc2 (max-params = 1)
    A 21:0 function MyFunc3 (max-params = 1)
    B 27:0 function myFunc4 (max-params = 2)
    A 28:2 function myFunc4, IfStatement (28:2-32:3) (max-depth = 1)
    A 29:7 function myFunc4, arrow function (29:7-31:5) (max-nested-callbacks = 1)
  Error: Complexity of code above maximum allowable rank C (3), messages - 1


  $ npx eslintcc --format json ./test/src/complexity__max_average_rank.js
  {"files":[{"file":"/development/github/eslintcc/test/src/complexity__max_average_rank.js","messages":[{"loc":{"start":{"line":3,"column":0},"end":{"line":5,"column":1}},"type":"function","name":"function MyFunc","rules":{"max-params":{"value":3,"rank":3,"label":"C"},"complexity":{"value":1,"rank":0.2,"label":"A"}},"maxRule":"max-params"}],"average":{"rank":3,"label":"C"}}],"average":{"rank":3,"label":"C"},"ranks":{"A":0,"B":0,"C":1,"D":0,"E":0,"F":0},"errors":{"maxRank":0,"maxAverageRank":true}}


  $ npx eslintcc --show-rules ./test/src/custom_parser/typescript-eslint-parser.ts
  A test/src/custom_parser/typescript-eslint-parser.ts
    A 6:7 function test (max-params = 1)
    A 7:4 function test, IfStatement (7:4-11:5) (max-depth = 1)

Node.js API

While ESLintСС is designed to be run on the command line, it’s possible to use ESLintСС programmatically through the Node.js API. The purpose of the Node.js API is to allow plugin and tool authors to use the ESLintСС functionality directly, without going through the command line interface.

Complexity class

Is a main class for use in Node.js applications.

Example

const { Complexity } = require('eslintcc');

const complexity = new Complexity({
  rules: 'logic',
  eslintOptions: {
    useEslintrc: false,
    overrideConfig: {
      parser: '@typescript-eslint/parser',
      plugins: ['@typescript-eslint'],
      extends: ['eslint:recommended', 'plugin:@typescript-eslint/recommended']
    }
  }
});
const report = await complexity.lintFiles(['yourfile.ts']);

console.log(JSON.stringify(report, null, '\t'));

new Complexity(options)

Class options equivalent to the command line (see Command line options):

• options.rules, Default: ‘logic’
• options.greaterThan, Default: undefined
• options.lessThan, Default: undefined
• options.noInlineConfig, Default: false
• options.maxRank, Default: ‘C’
• options.maxAverageRank, Default: ‘B’

Additional options available in API mode:

• options.ranks, Default: null - Allows you to set an arbitrary comparison of ranks and max counters of indicators of the corresponding rules.

Example:

const complexity = new Complexity({
  ranks: {
    'complexity': { A: 5, B: 10, C: 20, D: 30, E: 40, F: Infinity }
    'max-depth': { A: 2, B: 3, C: 4, D: 6, E: 8, F: Infinity}
  }
})

• options.eslintOptions, Default: {} - This option allows you to configure the internal ESLint class. It’s allows you to set additional options described in the documentation: ESLint: Node.js API

complexity.lintFiles(patterns)

This method lints the files that match the glob patterns and then returns the results.

Parameters

• patterns (string | string[]) - The lint target files. This can contain any of file paths, directory paths, and glob patterns.

Return Value

Promise<ComplexityResult> - The promise that will be fulfilled with an ComplexityResult object.

Example:

{
  'average': { 'rank': 0.2, 'label': 'A' },
  'errors': {
    'maxAverageRank': false,
    'maxRank': 0
  },
  'ranks': {
    'A': 1,
    'B': 0,
    'C': 0,
    'D': 0,
    'E': 0,
    'F': 0
  },
  'files': [{
    'average': { 'rank': 0.2, 'label': 'A' },
    'file': ...absolute path to file...,
    'messages': [{
      'type': 'function',
      'loc': { 'start': { 'line': 3, 'column': 0 }, 'end': { 'line': 5, 'column': 1 } },
      'name': 'function myFunc',
      'rules': { 'complexity': { 'value': 1, 'rank': 0.2, 'label': 'A' } },
      'maxRule': 'complexity'
    }]
  }]
}