eslint/lib/rules/no-negated-condition.js

   1 /**
   2  * @fileoverview Rule to disallow a negated condition
   3  * @author Alberto Rodríguez
   4  */
   5 "use strict";
   6
   7 //------------------------------------------------------------------------------
   8 // Rule Definition
   9 //------------------------------------------------------------------------------
  10
  11 module.exports = {
  12     meta: {
  13         type: "suggestion",
  14
  15         docs: {
  16             description: "disallow negated conditions",
  17             recommended: false,
  18             url: "https://eslint.org/docs/rules/no-negated-condition"
  19         },
  20
  21         schema: [],
  22
  23         messages: {
  24             unexpectedNegated: "Unexpected negated condition."
  25         }
  26     },
  27
  28     create(context) {
  29
  30         /**
  31          * Determines if a given node is an if-else without a condition on the else
  32          * @param {ASTNode} node The node to check.
  33          * @returns {boolean} True if the node has an else without an if.
  34          * @private
  35          */
  36         function hasElseWithoutCondition(node) {
  37             return node.alternate && node.alternate.type !== "IfStatement";
  38         }
  39
  40         /**
  41          * Determines if a given node is a negated unary expression
  42          * @param {Object} test The test object to check.
  43          * @returns {boolean} True if the node is a negated unary expression.
  44          * @private
  45          */
  46         function isNegatedUnaryExpression(test) {
  47             return test.type === "UnaryExpression" && test.operator === "!";
  48         }
  49
  50         /**
  51          * Determines if a given node is a negated binary expression
  52          * @param {Test} test The test to check.
  53          * @returns {boolean} True if the node is a negated binary expression.
  54          * @private
  55          */
  56         function isNegatedBinaryExpression(test) {
  57             return test.type === "BinaryExpression" &&
  58                 (test.operator === "!=" || test.operator === "!==");
  59         }
  60
  61         /**
  62          * Determines if a given node has a negated if expression
  63          * @param {ASTNode} node The node to check.
  64          * @returns {boolean} True if the node has a negated if expression.
  65          * @private
  66          */
  67         function isNegatedIf(node) {
  68             return isNegatedUnaryExpression(node.test) || isNegatedBinaryExpression(node.test);
  69         }
  70
  71         return {
  72             IfStatement(node) {
  73                 if (!hasElseWithoutCondition(node)) {
  74                     return;
  75                 }
  76
  77                 if (isNegatedIf(node)) {
  78                     context.report({
  79                         node,
  80                         messageId: "unexpectedNegated"
  81                     });
  82                 }
  83             },
  84             ConditionalExpression(node) {
  85                 if (isNegatedIf(node)) {
  86                     context.report({
  87                         node,
  88                         messageId: "unexpectedNegated"
  89                     });
  90                 }
  91             }
  92         };
  93     }
  94 };