eslint-rule-extender

A utility to extend existing ESLint rules.

Installation

npm install eslint-rule-extender

or

yarn add eslint-rule-extender

Usage

The default export is a function that takes two arguments and returns the modified rule.

API

ruleExtender(originalRule: ESLintRule, options: Object) => ESLintRule;

• originalRule - The original rule to extend
• options - An object with the desired overrides (options can be viewed below)

Example Usage

const ruleExtender = require('eslint-rule-extender');
const { originalRule } = require('eslint-plugin-example');

const extendedRule = ruleExtender(originalRule, options);

module.exports = {
  extendedRule,
};

Options

metaOverrides

Overrides for the original rule's meta property. The properties of the meta object can be found here.

const extendedRule = ruleExtender(originalRule, {
  metaOverrides: {
    type: 'suggestion',
    fixable: false,
  },
});

createAdditionalVisitors

A function that has the same signature as ESLint rules' create method. It is passed the context object and should return an object of visitor callbacks. See the official ESLint docs for more details!

Note that this will not override existing visitors with the same node names. To modify an existing visitor's report results, please use reportOverrides.

Example Usage

const extendedRule = ruleExtender(originalRule, {
  createAdditionalVisitors(context) {
    return {
      ArrowFunctionExpression(node) {
        context.report({ node, messageId: 'anAdditionalSuggestion' });
      },
    };
  },
});

reportOverrides

A function that is called with the report metadata of the original rule's context.report() calls and a modified context object. The return value of this function is a trinary with the following behavior:

• true: report with original metadata (unchanged)
• false: do not report
• modified report metadata object: report with this metadata instead

Example Usage

const extendedRule = ruleExtender(originalRule, {
  reportOverrides(meta, context) {
    if (
      meta.node.type === 'FunctionExpression' 
        && context.options[1].ignoreFunctionExpression
    ) {
      // These reports will be filtered out.
      return false;
    }
    
    if (
        meta.node.parent.arguments[0] === meta.node
          && meta.node.parent.type === 'CallExpression' 
          && meta.node.parent.callee.type === 'Identifier' 
          && meta.node.parent.callee.name === context.options[1].disallowedCallExpressionName
    ) {
      // Report with this metadata instead.
      return {
        ...meta,
        node: meta.node.parent,
        message: `${meta.node.parent.callee.name} no longer supports a callback for the first argument.`,
      };
    }
    
    // Otherwise, report as usual.
    return true;
  },
});

Putting It All Together

const ruleExtender = require('eslint-rule-extender');
const { originalRule } = require('eslint-plugin-example');

const extendedRule = ruleExtender(originalRule, {
  metaOverrides: {
    type: 'suggestion',
    fixable: false,
  },
  createAdditionalVisitors(context) {
    return {
      ArrowFunctionExpression(node) {
        context.report({ node, messageId: 'anAdditionalSuggestion' });
      },
    };
  },
  reportOverrides(meta) {
    return meta.node.type !== 'ThisExpression';
  },
});

module.exports = {
  extendedRule,
};

Prior art

• eslint-rule-composer