eslint/lib/rules/no-self-compare.js

   1 /**
   2  * @fileoverview Rule to flag comparison where left part is the same as the right
   3  * part.
   4  * @author Ilya Volodin
   5  */
   6
   7 "use strict";
   8
   9 //------------------------------------------------------------------------------
  10 // Rule Definition
  11 //------------------------------------------------------------------------------
  12
  13 module.exports = {
  14     meta: {
  15         type: "problem",
  16
  17         docs: {
  18             description: "disallow comparisons where both sides are exactly the same",
  19             recommended: false,
  20             url: "https://eslint.org/docs/rules/no-self-compare"
  21         },
  22
  23         schema: [],
  24
  25         messages: {
  26             comparingToSelf: "Comparing to itself is potentially pointless."
  27         }
  28     },
  29
  30     create(context) {
  31         const sourceCode = context.getSourceCode();
  32
  33         /**
  34          * Determines whether two nodes are composed of the same tokens.
  35          * @param {ASTNode} nodeA The first node
  36          * @param {ASTNode} nodeB The second node
  37          * @returns {boolean} true if the nodes have identical token representations
  38          */
  39         function hasSameTokens(nodeA, nodeB) {
  40             const tokensA = sourceCode.getTokens(nodeA);
  41             const tokensB = sourceCode.getTokens(nodeB);
  42
  43             return tokensA.length === tokensB.length &&
  44                 tokensA.every((token, index) => token.type === tokensB[index].type && token.value === tokensB[index].value);
  45         }
  46
  47         return {
  48
  49             BinaryExpression(node) {
  50                 const operators = new Set(["===", "==", "!==", "!=", ">", "<", ">=", "<="]);
  51
  52                 if (operators.has(node.operator) && hasSameTokens(node.left, node.right)) {
  53                     context.report({ node, messageId: "comparingToSelf" });
  54                 }
  55             }
  56         };
  57
  58     }
  59 };