1 | /**
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2 | * @fileoverview Rule to enforce that all class methods use 'this'.
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3 | * @author Patrick Williams
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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 | //------------------------------------------------------------------------------
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9 | // Requirements
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10 | //------------------------------------------------------------------------------
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11 |
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12 | const astUtils = require("./utils/ast-utils");
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13 |
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14 | //------------------------------------------------------------------------------
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15 | // Rule Definition
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16 | //------------------------------------------------------------------------------
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17 |
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18 | module.exports = {
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19 | meta: {
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20 | type: "suggestion",
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21 |
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22 | docs: {
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23 | description: "enforce that class methods utilize `this`",
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24 | category: "Best Practices",
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25 | recommended: false,
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26 | url: "https://eslint.org/docs/rules/class-methods-use-this"
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27 | },
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28 |
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29 | schema: [{
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30 | type: "object",
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31 | properties: {
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32 | exceptMethods: {
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33 | type: "array",
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34 | items: {
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35 | type: "string"
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36 | }
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37 | }
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38 | },
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39 | additionalProperties: false
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40 | }],
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41 |
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42 | messages: {
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43 | missingThis: "Expected 'this' to be used by class {{name}}."
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44 | }
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45 | },
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46 | create(context) {
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47 | const config = Object.assign({}, context.options[0]);
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48 | const exceptMethods = new Set(config.exceptMethods || []);
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49 |
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50 | const stack = [];
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51 |
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52 | /**
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53 | * Initializes the current context to false and pushes it onto the stack.
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54 | * These booleans represent whether 'this' has been used in the context.
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55 | * @returns {void}
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56 | * @private
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57 | */
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58 | function enterFunction() {
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59 | stack.push(false);
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60 | }
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61 |
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62 | /**
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63 | * Check if the node is an instance method
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64 | * @param {ASTNode} node node to check
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65 | * @returns {boolean} True if its an instance method
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66 | * @private
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67 | */
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68 | function isInstanceMethod(node) {
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69 | return !node.static && node.kind !== "constructor" && node.type === "MethodDefinition";
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70 | }
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71 |
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72 | /**
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73 | * Check if the node is an instance method not excluded by config
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74 | * @param {ASTNode} node node to check
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75 | * @returns {boolean} True if it is an instance method, and not excluded by config
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76 | * @private
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77 | */
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78 | function isIncludedInstanceMethod(node) {
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79 | return isInstanceMethod(node) &&
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80 | (node.computed || !exceptMethods.has(node.key.name));
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81 | }
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82 |
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83 | /**
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84 | * Checks if we are leaving a function that is a method, and reports if 'this' has not been used.
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85 | * Static methods and the constructor are exempt.
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86 | * Then pops the context off the stack.
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87 | * @param {ASTNode} node A function node that was entered.
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88 | * @returns {void}
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89 | * @private
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90 | */
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91 | function exitFunction(node) {
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92 | const methodUsesThis = stack.pop();
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93 |
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94 | if (isIncludedInstanceMethod(node.parent) && !methodUsesThis) {
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95 | context.report({
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96 | node,
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97 | messageId: "missingThis",
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98 | data: {
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99 | name: astUtils.getFunctionNameWithKind(node)
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100 | }
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101 | });
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102 | }
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103 | }
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104 |
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105 | /**
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106 | * Mark the current context as having used 'this'.
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107 | * @returns {void}
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108 | * @private
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109 | */
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110 | function markThisUsed() {
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111 | if (stack.length) {
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112 | stack[stack.length - 1] = true;
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113 | }
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114 | }
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115 |
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116 | return {
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117 | FunctionDeclaration: enterFunction,
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118 | "FunctionDeclaration:exit": exitFunction,
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119 | FunctionExpression: enterFunction,
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120 | "FunctionExpression:exit": exitFunction,
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121 | ThisExpression: markThisUsed,
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122 | Super: markThisUsed
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123 | };
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124 | }
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125 | };
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