noStringOperator.js

/* eslint-disable */
const {ESLintUtils} = require('@typescript-eslint/experimental-utils');
const TS = require('typescript');
const TSUtils = require('tsutils');

module.exports = ESLintUtils.RuleCreator.withoutDocs({
  meta: {
    type: 'problem',
    docs: {
      description: 'Bans using binary operators on string types'
    },
    messages: {
      noStringOperator: 'Do not use binary operators on string types.'
    }
  },
  defaultOptions: [],
  create: (context) => {
    return {
      BinaryExpression: (node) => {
        if (node.operator === '===' || node.operator === '==' || node.operator === '!==' || node.operator === '!=') {
          return;
        }

        const parserServices = ESLintUtils.getParserServices(context);
        const checker = parserServices.program.getTypeChecker();

        const originalRightNode = parserServices.esTreeNodeToTSNodeMap.get(node.right);
        const originalLeftNode = parserServices.esTreeNodeToTSNodeMap.get(node.left);
        const rightNodeType = checker.getTypeAtLocation(originalRightNode);
        const leftNodeType = checker.getTypeAtLocation(originalLeftNode);

        if (TSUtils.isTypeFlagSet(rightNodeType, TS.TypeFlags.StringLike) || TSUtils.isTypeFlagSet(leftNodeType, TS.TypeFlags.StringLike)) {
          context.report({
            messageId: 'noStringOperator',
            node: node.right
          });
        }
      }
    };
  }
});