2 * @fileoverview Rule to flag the use of redundant constructors in classes.
3 * @author Alberto RodrÃguez
7 //------------------------------------------------------------------------------
9 //------------------------------------------------------------------------------
12 * Checks whether a given array of statements is a single call of `super`.
13 * @param {ASTNode[]} body An array of statements to check.
14 * @returns {boolean} `true` if the body is a single call of `super`.
16 function isSingleSuperCall(body) {
19 body[0].type === "ExpressionStatement" &&
20 body[0].expression.type === "CallExpression" &&
21 body[0].expression.callee.type === "Super"
26 * Checks whether a given node is a pattern which doesn't have any side effects.
27 * Default parameters and Destructuring parameters can have side effects.
28 * @param {ASTNode} node A pattern node.
29 * @returns {boolean} `true` if the node doesn't have any side effects.
31 function isSimple(node) {
32 return node.type === "Identifier" || node.type === "RestElement";
36 * Checks whether a given array of expressions is `...arguments` or not.
37 * `super(...arguments)` passes all arguments through.
38 * @param {ASTNode[]} superArgs An array of expressions to check.
39 * @returns {boolean} `true` if the superArgs is `...arguments`.
41 function isSpreadArguments(superArgs) {
43 superArgs.length === 1 &&
44 superArgs[0].type === "SpreadElement" &&
45 superArgs[0].argument.type === "Identifier" &&
46 superArgs[0].argument.name === "arguments"
51 * Checks whether given 2 nodes are identifiers which have the same name or not.
52 * @param {ASTNode} ctorParam A node to check.
53 * @param {ASTNode} superArg A node to check.
54 * @returns {boolean} `true` if the nodes are identifiers which have the same
57 function isValidIdentifierPair(ctorParam, superArg) {
59 ctorParam.type === "Identifier" &&
60 superArg.type === "Identifier" &&
61 ctorParam.name === superArg.name
66 * Checks whether given 2 nodes are a rest/spread pair which has the same values.
67 * @param {ASTNode} ctorParam A node to check.
68 * @param {ASTNode} superArg A node to check.
69 * @returns {boolean} `true` if the nodes are a rest/spread pair which has the
72 function isValidRestSpreadPair(ctorParam, superArg) {
74 ctorParam.type === "RestElement" &&
75 superArg.type === "SpreadElement" &&
76 isValidIdentifierPair(ctorParam.argument, superArg.argument)
81 * Checks whether given 2 nodes have the same value or not.
82 * @param {ASTNode} ctorParam A node to check.
83 * @param {ASTNode} superArg A node to check.
84 * @returns {boolean} `true` if the nodes have the same value or not.
86 function isValidPair(ctorParam, superArg) {
88 isValidIdentifierPair(ctorParam, superArg) ||
89 isValidRestSpreadPair(ctorParam, superArg)
94 * Checks whether the parameters of a constructor and the arguments of `super()`
95 * have the same values or not.
96 * @param {ASTNode} ctorParams The parameters of a constructor to check.
97 * @param {ASTNode} superArgs The arguments of `super()` to check.
98 * @returns {boolean} `true` if those have the same values.
100 function isPassingThrough(ctorParams, superArgs) {
101 if (ctorParams.length !== superArgs.length) {
105 for (let i = 0; i < ctorParams.length; ++i) {
106 if (!isValidPair(ctorParams[i], superArgs[i])) {
115 * Checks whether the constructor body is a redundant super call.
116 * @param {Array} body constructor body content.
117 * @param {Array} ctorParams The params to check against super call.
118 * @returns {boolean} true if the constructor body is redundant
120 function isRedundantSuperCall(body, ctorParams) {
122 isSingleSuperCall(body) &&
123 ctorParams.every(isSimple) &&
125 isSpreadArguments(body[0].expression.arguments) ||
126 isPassingThrough(ctorParams, body[0].expression.arguments)
131 //------------------------------------------------------------------------------
133 //------------------------------------------------------------------------------
140 description: "disallow unnecessary constructors",
141 category: "ECMAScript 6",
143 url: "https://eslint.org/docs/rules/no-useless-constructor"
149 noUselessConstructor: "Useless constructor."
156 * Checks whether a node is a redundant constructor
157 * @param {ASTNode} node node to check
160 function checkForConstructor(node) {
161 if (node.kind !== "constructor") {
166 * Prevent crashing on parsers which do not require class constructor
167 * to have a body, e.g. typescript and flow
169 if (!node.value.body) {
173 const body = node.value.body.body;
174 const ctorParams = node.value.params;
175 const superClass = node.parent.parent.superClass;
177 if (superClass ? isRedundantSuperCall(body, ctorParams) : (body.length === 0)) {
180 messageId: "noUselessConstructor"
186 MethodDefinition: checkForConstructor