2 * @fileoverview Prefer destructuring from arrays and objects
3 * @author Alex LaFroscia
7 //------------------------------------------------------------------------------
9 //------------------------------------------------------------------------------
11 const astUtils = require("./utils/ast-utils");
13 //------------------------------------------------------------------------------
15 //------------------------------------------------------------------------------
17 const PRECEDENCE_OF_ASSIGNMENT_EXPR = astUtils.getPrecedence({ type: "AssignmentExpression" });
19 //------------------------------------------------------------------------------
21 //------------------------------------------------------------------------------
28 description: "require destructuring from arrays and/or objects",
29 category: "ECMAScript 6",
31 url: "https://eslint.org/docs/rules/prefer-destructuring"
40 * old support {array: Boolean, object: Boolean}
41 * new support {VariableDeclarator: {}, AssignmentExpression: {}}
57 additionalProperties: false
59 AssignmentExpression: {
69 additionalProperties: false
72 additionalProperties: false
84 additionalProperties: false
91 enforceForRenamedProperties: {
95 additionalProperties: false
100 preferDestructuring: "Use {{type}} destructuring."
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 }
113 normalizedOptions = typeof enabledTypes.array !== "undefined" || typeof enabledTypes.object !== "undefined"
114 ? { VariableDeclarator: enabledTypes, AssignmentExpression: enabledTypes }
118 //--------------------------------------------------------------------------
120 //--------------------------------------------------------------------------
122 // eslint-disable-next-line jsdoc/require-description
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
128 function shouldCheck(nodeType, destructuringType) {
129 return normalizedOptions &&
130 normalizedOptions[nodeType] &&
131 normalizedOptions[nodeType][destructuringType];
135 * Determines if the given node is accessing an array index
137 * This is used to differentiate array index access from object property
139 * @param {ASTNode} node the node to evaluate
140 * @returns {boolean} whether or not the node is an integer
142 function isArrayIndexAccess(node) {
143 return Number.isInteger(node.property.value);
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
153 function report(reportNode, type, fix) {
156 messageId: "preferDestructuring",
163 * Determines if a node should be fixed into object destructuring
165 * The fixer only fixes the simplest case of object destructuring,
166 * like: `let x = a.x`;
168 * Assignment expression is not fixed.
169 * Array destructuring is not fixed.
170 * Renamed property is not fixed.
171 * @param {ASTNode} node the node to evaluate
172 * @returns {boolean} whether or not the node should be fixed
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;
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
191 function fixIntoObjectDestructuring(fixer, node) {
192 const rightNode = node.init;
193 const sourceCode = context.getSourceCode();
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) {
200 let objectText = sourceCode.getText(rightNode.object);
202 if (astUtils.getPrecedence(rightNode.object) < PRECEDENCE_OF_ASSIGNMENT_EXPR) {
203 objectText = `(${objectText})`;
206 return fixer.replaceText(
208 `{${rightNode.property.name}} = ${objectText}`
213 * Check that the `prefer-destructuring` rules are followed based on the
214 * given left- and right-hand side of the assignment.
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
223 function performCheck(leftNode, rightNode, reportNode) {
224 if (rightNode.type !== "MemberExpression" || rightNode.object.type === "Super") {
228 if (isArrayIndexAccess(rightNode)) {
229 if (shouldCheck(reportNode.type, "array")) {
230 report(reportNode, "array", null);
235 const fix = shouldFix(reportNode)
236 ? fixer => fixIntoObjectDestructuring(fixer, reportNode)
239 if (shouldCheck(reportNode.type, "object") && enforceForRenamedProperties) {
240 report(reportNode, "object", fix);
244 if (shouldCheck(reportNode.type, "object")) {
245 const property = rightNode.property;
248 (property.type === "Literal" && leftNode.name === property.value) ||
249 (property.type === "Identifier" && leftNode.name === property.name && !rightNode.computed)
251 report(reportNode, "object", fix);
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
262 function checkVariableDeclarator(node) {
264 // Skip if variable is declared without assignment
269 // We only care about member expressions past this point
270 if (node.init.type !== "MemberExpression") {
274 performCheck(node.id, node.init, node);
278 * Run the `prefer-destructuring` check on an AssignmentExpression
279 * @param {ASTNode} node the AssignmentExpression node
282 function checkAssignmentExpression(node) {
283 if (node.operator === "=") {
284 performCheck(node.left, node.right, node);
288 //--------------------------------------------------------------------------
290 //--------------------------------------------------------------------------
293 VariableDeclarator: checkVariableDeclarator,
294 AssignmentExpression: checkAssignmentExpression