1 | /**
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2 | * @fileoverview Rule to disallow a negated condition
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3 | * @author Alberto Rodríguez
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4 | */
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5 | ;
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6 |
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7 | //------------------------------------------------------------------------------
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8 | // Rule Definition
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9 | //------------------------------------------------------------------------------
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10 |
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11 | module.exports = {
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12 | meta: {
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13 | type: "suggestion",
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14 |
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15 | docs: {
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16 | description: "disallow negated conditions",
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17 | category: "Stylistic Issues",
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18 | recommended: false,
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19 | url: "https://eslint.org/docs/rules/no-negated-condition"
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20 | },
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21 |
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22 | schema: [],
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23 |
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24 | messages: {
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25 | unexpectedNegated: "Unexpected negated condition."
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26 | }
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27 | },
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28 |
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29 | create(context) {
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30 |
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31 | /**
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32 | * Determines if a given node is an if-else without a condition on the else
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33 | * @param {ASTNode} node The node to check.
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34 | * @returns {boolean} True if the node has an else without an if.
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35 | * @private
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36 | */
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37 | function hasElseWithoutCondition(node) {
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38 | return node.alternate && node.alternate.type !== "IfStatement";
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39 | }
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40 |
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41 | /**
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42 | * Determines if a given node is a negated unary expression
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43 | * @param {Object} test The test object to check.
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44 | * @returns {boolean} True if the node is a negated unary expression.
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45 | * @private
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46 | */
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47 | function isNegatedUnaryExpression(test) {
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48 | return test.type === "UnaryExpression" && test.operator === "!";
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49 | }
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50 |
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51 | /**
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52 | * Determines if a given node is a negated binary expression
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53 | * @param {Test} test The test to check.
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54 | * @returns {boolean} True if the node is a negated binary expression.
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55 | * @private
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56 | */
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57 | function isNegatedBinaryExpression(test) {
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58 | return test.type === "BinaryExpression" &&
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59 | (test.operator === "!=" || test.operator === "!==");
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60 | }
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61 |
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62 | /**
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63 | * Determines if a given node has a negated if expression
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64 | * @param {ASTNode} node The node to check.
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65 | * @returns {boolean} True if the node has a negated if expression.
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66 | * @private
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67 | */
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68 | function isNegatedIf(node) {
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69 | return isNegatedUnaryExpression(node.test) || isNegatedBinaryExpression(node.test);
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70 | }
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71 |
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72 | return {
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73 | IfStatement(node) {
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74 | if (!hasElseWithoutCondition(node)) {
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75 | return;
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76 | }
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77 |
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78 | if (isNegatedIf(node)) {
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79 | context.report({
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80 | node,
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81 | messageId: "unexpectedNegated"
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82 | });
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83 | }
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84 | },
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85 | ConditionalExpression(node) {
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86 | if (isNegatedIf(node)) {
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87 | context.report({
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88 | node,
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89 | messageId: "unexpectedNegated"
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90 | });
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91 | }
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92 | }
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93 | };
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94 | }
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95 | };
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