1 | /**
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2 | * @fileoverview Rule to flag unnecessary bind calls
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3 | * @author Bence Dányi <bence@danyi.me>
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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 | // Requirements
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9 | //------------------------------------------------------------------------------
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10 |
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11 | const getPropertyName = require("../ast-utils").getStaticPropertyName;
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12 |
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13 | //------------------------------------------------------------------------------
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14 | // Rule Definition
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15 | //------------------------------------------------------------------------------
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16 |
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17 | module.exports = {
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18 | meta: {
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19 | docs: {
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20 | description: "disallow unnecessary calls to `.bind()`",
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21 | category: "Best Practices",
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22 | recommended: false
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23 | },
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24 |
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25 | schema: []
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26 | },
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27 |
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28 | create(context) {
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29 | let scopeInfo = null;
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30 |
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31 | /**
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32 | * Reports a given function node.
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33 | *
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34 | * @param {ASTNode} node - A node to report. This is a FunctionExpression or
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35 | * an ArrowFunctionExpression.
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36 | * @returns {void}
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37 | */
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38 | function report(node) {
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39 | context.report({
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40 | node: node.parent.parent,
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41 | message: "The function binding is unnecessary.",
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42 | loc: node.parent.property.loc.start
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43 | });
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44 | }
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45 |
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46 | /**
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47 | * Checks whether or not a given function node is the callee of `.bind()`
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48 | * method.
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49 | *
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50 | * e.g. `(function() {}.bind(foo))`
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51 | *
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52 | * @param {ASTNode} node - A node to report. This is a FunctionExpression or
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53 | * an ArrowFunctionExpression.
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54 | * @returns {boolean} `true` if the node is the callee of `.bind()` method.
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55 | */
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56 | function isCalleeOfBindMethod(node) {
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57 | const parent = node.parent;
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58 | const grandparent = parent.parent;
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59 |
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60 | return (
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61 | grandparent &&
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62 | grandparent.type === "CallExpression" &&
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63 | grandparent.callee === parent &&
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64 | grandparent.arguments.length === 1 &&
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65 | parent.type === "MemberExpression" &&
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66 | parent.object === node &&
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67 | getPropertyName(parent) === "bind"
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68 | );
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69 | }
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70 |
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71 | /**
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72 | * Adds a scope information object to the stack.
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73 | *
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74 | * @param {ASTNode} node - A node to add. This node is a FunctionExpression
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75 | * or a FunctionDeclaration node.
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76 | * @returns {void}
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77 | */
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78 | function enterFunction(node) {
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79 | scopeInfo = {
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80 | isBound: isCalleeOfBindMethod(node),
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81 | thisFound: false,
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82 | upper: scopeInfo
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83 | };
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84 | }
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85 |
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86 | /**
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87 | * Removes the scope information object from the top of the stack.
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88 | * At the same time, this reports the function node if the function has
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89 | * `.bind()` and the `this` keywords found.
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90 | *
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91 | * @param {ASTNode} node - A node to remove. This node is a
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92 | * FunctionExpression or a FunctionDeclaration node.
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93 | * @returns {void}
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94 | */
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95 | function exitFunction(node) {
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96 | if (scopeInfo.isBound && !scopeInfo.thisFound) {
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97 | report(node);
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98 | }
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99 |
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100 | scopeInfo = scopeInfo.upper;
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101 | }
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102 |
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103 | /**
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104 | * Reports a given arrow function if the function is callee of `.bind()`
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105 | * method.
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106 | *
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107 | * @param {ASTNode} node - A node to report. This node is an
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108 | * ArrowFunctionExpression.
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109 | * @returns {void}
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110 | */
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111 | function exitArrowFunction(node) {
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112 | if (isCalleeOfBindMethod(node)) {
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113 | report(node);
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114 | }
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115 | }
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116 |
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117 | /**
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118 | * Set the mark as the `this` keyword was found in this scope.
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119 | *
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120 | * @returns {void}
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121 | */
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122 | function markAsThisFound() {
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123 | if (scopeInfo) {
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124 | scopeInfo.thisFound = true;
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125 | }
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126 | }
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127 |
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128 | return {
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129 | "ArrowFunctionExpression:exit": exitArrowFunction,
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130 | FunctionDeclaration: enterFunction,
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131 | "FunctionDeclaration:exit": exitFunction,
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132 | FunctionExpression: enterFunction,
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133 | "FunctionExpression:exit": exitFunction,
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134 | ThisExpression: markAsThisFound
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135 | };
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136 | }
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137 | };
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