1/** 2 * @fileoverview Rule to disallow duplicate conditions in if-else-if chains 3 * @author Milos Djermanovic 4 */ 5 6"use strict"; 7 8//------------------------------------------------------------------------------ 9// Requirements 10//------------------------------------------------------------------------------ 11 12const astUtils = require("./utils/ast-utils"); 13 14//------------------------------------------------------------------------------ 15// Helpers 16//------------------------------------------------------------------------------ 17 18/** 19 * Determines whether the first given array is a subset of the second given array. 20 * @param {Function} comparator A function to compare two elements, should return `true` if they are equal. 21 * @param {Array} arrA The array to compare from. 22 * @param {Array} arrB The array to compare against. 23 * @returns {boolean} `true` if the array `arrA` is a subset of the array `arrB`. 24 */ 25function isSubsetByComparator(comparator, arrA, arrB) { 26 return arrA.every(a => arrB.some(b => comparator(a, b))); 27} 28 29/** 30 * Splits the given node by the given logical operator. 31 * @param {string} operator Logical operator `||` or `&&`. 32 * @param {ASTNode} node The node to split. 33 * @returns {ASTNode[]} Array of conditions that makes the node when joined by the operator. 34 */ 35function splitByLogicalOperator(operator, node) { 36 if (node.type === "LogicalExpression" && node.operator === operator) { 37 return [...splitByLogicalOperator(operator, node.left), ...splitByLogicalOperator(operator, node.right)]; 38 } 39 return [node]; 40} 41 42const splitByOr = splitByLogicalOperator.bind(null, "||"); 43const splitByAnd = splitByLogicalOperator.bind(null, "&&"); 44 45//------------------------------------------------------------------------------ 46// Rule Definition 47//------------------------------------------------------------------------------ 48 49module.exports = { 50 meta: { 51 type: "problem", 52 53 docs: { 54 description: "disallow duplicate conditions in if-else-if chains", 55 category: "Possible Errors", 56 recommended: true, 57 url: "https://eslint.org/docs/rules/no-dupe-else-if" 58 }, 59 60 schema: [], 61 62 messages: { 63 unexpected: "This branch can never execute. Its condition is a duplicate or covered by previous conditions in the if-else-if chain." 64 } 65 }, 66 67 create(context) { 68 const sourceCode = context.getSourceCode(); 69 70 /** 71 * Determines whether the two given nodes are considered to be equal. In particular, given that the nodes 72 * represent expressions in a boolean context, `||` and `&&` can be considered as commutative operators. 73 * @param {ASTNode} a First node. 74 * @param {ASTNode} b Second node. 75 * @returns {boolean} `true` if the nodes are considered to be equal. 76 */ 77 function equal(a, b) { 78 if (a.type !== b.type) { 79 return false; 80 } 81 82 if ( 83 a.type === "LogicalExpression" && 84 (a.operator === "||" || a.operator === "&&") && 85 a.operator === b.operator 86 ) { 87 return equal(a.left, b.left) && equal(a.right, b.right) || 88 equal(a.left, b.right) && equal(a.right, b.left); 89 } 90 91 return astUtils.equalTokens(a, b, sourceCode); 92 } 93 94 const isSubset = isSubsetByComparator.bind(null, equal); 95 96 return { 97 IfStatement(node) { 98 const test = node.test, 99 conditionsToCheck = test.type === "LogicalExpression" && test.operator === "&&" 100 ? [test, ...splitByAnd(test)] 101 : [test]; 102 let current = node, 103 listToCheck = conditionsToCheck.map(c => splitByOr(c).map(splitByAnd)); 104 105 while (current.parent && current.parent.type === "IfStatement" && current.parent.alternate === current) { 106 current = current.parent; 107 108 const currentOrOperands = splitByOr(current.test).map(splitByAnd); 109 110 listToCheck = listToCheck.map(orOperands => orOperands.filter( 111 orOperand => !currentOrOperands.some(currentOrOperand => isSubset(currentOrOperand, orOperand)) 112 )); 113 114 if (listToCheck.some(orOperands => orOperands.length === 0)) { 115 context.report({ node: test, messageId: "unexpected" }); 116 break; 117 } 118 } 119 } 120 }; 121 } 122}; 123