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