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 /** @type {import('../shared/types').Rule} */
  14 module.exports = {
  15     meta: {
  16         type: "problem",
  17
  18         docs: {
  19             description: "disallow comparisons where both sides are exactly the same",
  20             recommended: false,
  21             url: "https://eslint.org/docs/rules/no-self-compare"
  22         },
  23
  24         schema: [],
  25
  26         messages: {
  27             comparingToSelf: "Comparing to itself is potentially pointless."
  28         }
  29     },
  30
  31     create(context) {
  32         const sourceCode = context.getSourceCode();
  33
  34         /**
  35          * Determines whether two nodes are composed of the same tokens.
  36          * @param {ASTNode} nodeA The first node
  37          * @param {ASTNode} nodeB The second node
  38          * @returns {boolean} true if the nodes have identical token representations
  39          */
  40         function hasSameTokens(nodeA, nodeB) {
  41             const tokensA = sourceCode.getTokens(nodeA);
  42             const tokensB = sourceCode.getTokens(nodeB);
  43
  44             return tokensA.length === tokensB.length &&
  45                 tokensA.every((token, index) => token.type === tokensB[index].type && token.value === tokensB[index].value);
  46         }
  47
  48         return {
  49
  50             BinaryExpression(node) {
  51                 const operators = new Set(["===", "==", "!==", "!=", ">", "<", ">=", "<="]);
  52
  53                 if (operators.has(node.operator) && hasSameTokens(node.left, node.right)) {
  54                     context.report({ node, messageId: "comparingToSelf" });
  55                 }
  56             }
  57         };
  58
  59     }
  60 };