eslint/lib/rules/prefer-destructuring.js

   1 /**
   2  * @fileoverview Prefer destructuring from arrays and objects
   3  * @author Alex LaFroscia
   4  */
   5 "use strict";
   6
   7 //------------------------------------------------------------------------------
   8 // Requirements
   9 //------------------------------------------------------------------------------
  10
  11 const astUtils = require("./utils/ast-utils");
  12
  13 //------------------------------------------------------------------------------
  14 // Helpers
  15 //------------------------------------------------------------------------------
  16
  17 const PRECEDENCE_OF_ASSIGNMENT_EXPR = astUtils.getPrecedence({ type: "AssignmentExpression" });
  18
  19 //------------------------------------------------------------------------------
  20 // Rule Definition
  21 //------------------------------------------------------------------------------
  22
  23 module.exports = {
  24     meta: {
  25         type: "suggestion",
  26
  27         docs: {
  28             description: "require destructuring from arrays and/or objects",
  29             category: "ECMAScript 6",
  30             recommended: false,
  31             url: "https://eslint.org/docs/rules/prefer-destructuring"
  32         },
  33
  34         fixable: "code",
  35
  36         schema: [
  37             {
  38
  39                 /*
  40                  * old support {array: Boolean, object: Boolean}
  41                  * new support {VariableDeclarator: {}, AssignmentExpression: {}}
  42                  */
  43                 oneOf: [
  44                     {
  45                         type: "object",
  46                         properties: {
  47                             VariableDeclarator: {
  48                                 type: "object",
  49                                 properties: {
  50                                     array: {
  51                                         type: "boolean"
  52                                     },
  53                                     object: {
  54                                         type: "boolean"
  55                                     }
  56                                 },
  57                                 additionalProperties: false
  58                             },
  59                             AssignmentExpression: {
  60                                 type: "object",
  61                                 properties: {
  62                                     array: {
  63                                         type: "boolean"
  64                                     },
  65                                     object: {
  66                                         type: "boolean"
  67                                     }
  68                                 },
  69                                 additionalProperties: false
  70                             }
  71                         },
  72                         additionalProperties: false
  73                     },
  74                     {
  75                         type: "object",
  76                         properties: {
  77                             array: {
  78                                 type: "boolean"
  79                             },
  80                             object: {
  81                                 type: "boolean"
  82                             }
  83                         },
  84                         additionalProperties: false
  85                     }
  86                 ]
  87             },
  88             {
  89                 type: "object",
  90                 properties: {
  91                     enforceForRenamedProperties: {
  92                         type: "boolean"
  93                     }
  94                 },
  95                 additionalProperties: false
  96             }
  97         ],
  98
  99         messages: {
 100             preferDestructuring: "Use {{type}} destructuring."
 101         }
 102     },
 103     create(context) {
 104
 105         const enabledTypes = context.options[0];
 106         const enforceForRenamedProperties = context.options[1] && context.options[1].enforceForRenamedProperties;
 107         let normalizedOptions = {
 108             VariableDeclarator: { array: true, object: true },
 109             AssignmentExpression: { array: true, object: true }
 110         };
 111
 112         if (enabledTypes) {
 113             normalizedOptions = typeof enabledTypes.array !== "undefined" || typeof enabledTypes.object !== "undefined"
 114                 ? { VariableDeclarator: enabledTypes, AssignmentExpression: enabledTypes }
 115                 : enabledTypes;
 116         }
 117
 118         //--------------------------------------------------------------------------
 119         // Helpers
 120         //--------------------------------------------------------------------------
 121
 122         // eslint-disable-next-line jsdoc/require-description
 123         /**
 124          * @param {string} nodeType "AssignmentExpression" or "VariableDeclarator"
 125          * @param {string} destructuringType "array" or "object"
 126          * @returns {boolean} `true` if the destructuring type should be checked for the given node
 127          */
 128         function shouldCheck(nodeType, destructuringType) {
 129             return normalizedOptions &&
 130                 normalizedOptions[nodeType] &&
 131                 normalizedOptions[nodeType][destructuringType];
 132         }
 133
 134         /**
 135          * Determines if the given node is accessing an array index
 136          *
 137          * This is used to differentiate array index access from object property
 138          * access.
 139          * @param {ASTNode} node the node to evaluate
 140          * @returns {boolean} whether or not the node is an integer
 141          */
 142         function isArrayIndexAccess(node) {
 143             return Number.isInteger(node.property.value);
 144         }
 145
 146         /**
 147          * Report that the given node should use destructuring
 148          * @param {ASTNode} reportNode the node to report
 149          * @param {string} type the type of destructuring that should have been done
 150          * @param {Function|null} fix the fix function or null to pass to context.report
 151          * @returns {void}
 152          */
 153         function report(reportNode, type, fix) {
 154             context.report({
 155                 node: reportNode,
 156                 messageId: "preferDestructuring",
 157                 data: { type },
 158                 fix
 159             });
 160         }
 161
 162         /**
 163          * Determines if a node should be fixed into object destructuring
 164          *
 165          * The fixer only fixes the simplest case of object destructuring,
 166          * like: `let x = a.x`;
 167          *
 168          * Assignment expression is not fixed.
 169          * Array destructuring is not fixed.
 170          * Renamed property is not fixed.
 171          * @param {ASTNode} node the the node to evaluate
 172          * @returns {boolean} whether or not the node should be fixed
 173          */
 174         function shouldFix(node) {
 175             return node.type === "VariableDeclarator" &&
 176                 node.id.type === "Identifier" &&
 177                 node.init.type === "MemberExpression" &&
 178                 !node.init.computed &&
 179                 node.init.property.type === "Identifier" &&
 180                 node.id.name === node.init.property.name;
 181         }
 182
 183         /**
 184          * Fix a node into object destructuring.
 185          * This function only handles the simplest case of object destructuring,
 186          * see {@link shouldFix}.
 187          * @param {SourceCodeFixer} fixer the fixer object
 188          * @param {ASTNode} node the node to be fixed.
 189          * @returns {Object} a fix for the node
 190          */
 191         function fixIntoObjectDestructuring(fixer, node) {
 192             const rightNode = node.init;
 193             const sourceCode = context.getSourceCode();
 194
 195             // Don't fix if that would remove any comments. Only comments inside `rightNode.object` can be preserved.
 196             if (sourceCode.getCommentsInside(node).length > sourceCode.getCommentsInside(rightNode.object).length) {
 197                 return null;
 198             }
 199
 200             let objectText = sourceCode.getText(rightNode.object);
 201
 202             if (astUtils.getPrecedence(rightNode.object) < PRECEDENCE_OF_ASSIGNMENT_EXPR) {
 203                 objectText = `(${objectText})`;
 204             }
 205
 206             return fixer.replaceText(
 207                 node,
 208                 `{${rightNode.property.name}} = ${objectText}`
 209             );
 210         }
 211
 212         /**
 213          * Check that the `prefer-destructuring` rules are followed based on the
 214          * given left- and right-hand side of the assignment.
 215          *
 216          * Pulled out into a separate method so that VariableDeclarators and
 217          * AssignmentExpressions can share the same verification logic.
 218          * @param {ASTNode} leftNode the left-hand side of the assignment
 219          * @param {ASTNode} rightNode the right-hand side of the assignment
 220          * @param {ASTNode} reportNode the node to report the error on
 221          * @returns {void}
 222          */
 223         function performCheck(leftNode, rightNode, reportNode) {
 224             if (rightNode.type !== "MemberExpression" || rightNode.object.type === "Super") {
 225                 return;
 226             }
 227
 228             if (isArrayIndexAccess(rightNode)) {
 229                 if (shouldCheck(reportNode.type, "array")) {
 230                     report(reportNode, "array", null);
 231                 }
 232                 return;
 233             }
 234
 235             const fix = shouldFix(reportNode)
 236                 ? fixer => fixIntoObjectDestructuring(fixer, reportNode)
 237                 : null;
 238
 239             if (shouldCheck(reportNode.type, "object") && enforceForRenamedProperties) {
 240                 report(reportNode, "object", fix);
 241                 return;
 242             }
 243
 244             if (shouldCheck(reportNode.type, "object")) {
 245                 const property = rightNode.property;
 246
 247                 if (
 248                     (property.type === "Literal" && leftNode.name === property.value) ||
 249                     (property.type === "Identifier" && leftNode.name === property.name && !rightNode.computed)
 250                 ) {
 251                     report(reportNode, "object", fix);
 252                 }
 253             }
 254         }
 255
 256         /**
 257          * Check if a given variable declarator is coming from an property access
 258          * that should be using destructuring instead
 259          * @param {ASTNode} node the variable declarator to check
 260          * @returns {void}
 261          */
 262         function checkVariableDeclarator(node) {
 263
 264             // Skip if variable is declared without assignment
 265             if (!node.init) {
 266                 return;
 267             }
 268
 269             // We only care about member expressions past this point
 270             if (node.init.type !== "MemberExpression") {
 271                 return;
 272             }
 273
 274             performCheck(node.id, node.init, node);
 275         }
 276
 277         /**
 278          * Run the `prefer-destructuring` check on an AssignmentExpression
 279          * @param {ASTNode} node the AssignmentExpression node
 280          * @returns {void}
 281          */
 282         function checkAssignmentExpression(node) {
 283             if (node.operator === "=") {
 284                 performCheck(node.left, node.right, node);
 285             }
 286         }
 287
 288         //--------------------------------------------------------------------------
 289         // Public
 290         //--------------------------------------------------------------------------
 291
 292         return {
 293             VariableDeclarator: checkVariableDeclarator,
 294             AssignmentExpression: checkAssignmentExpression
 295         };
 296     }
 297 };