Example of a custom ESLint rule

no-bacon.js

/**
 * @fileoverview Don't allow bacon in variable names
 * @author Mike Solomon
 */
"use strict";

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

/** @type {import('eslint').Rule.RuleModule} */
module.exports = {
  meta: {
    type: 'suggestion',

    docs: {
      description: "Don't allow bacon in identifiers",
      recommended: false,
      url: "https://eslint.org/docs/rules/no-bacon",
    },

    schema: [], // no options

    messages: {
      avoidBacon: "The word bacon was found in '{{identifier}}'"
    }
  },

  create(context) {
    return {
      Identifier(node) {
        const identifier = node.name;

        if (identifier.toLowerCase().includes("bacon")) {
          context.report({
            node: node,
            messageId: 'avoidBacon',
            data: {
              identifier
            }
          });
        }
      }
    };
  },
};