eslint/lib/rules/no-useless-call.js

   1 /**
   2  * @fileoverview A rule to disallow unnecessary `.call()` and `.apply()`.
   3  * @author Toru Nagashima
   4  */
   5
   6 "use strict";
   7
   8 const astUtils = require("./utils/ast-utils");
   9
  10 //------------------------------------------------------------------------------
  11 // Helpers
  12 //------------------------------------------------------------------------------
  13
  14 /**
  15  * Checks whether or not a node is a `.call()`/`.apply()`.
  16  * @param {ASTNode} node A CallExpression node to check.
  17  * @returns {boolean} Whether or not the node is a `.call()`/`.apply()`.
  18  */
  19 function isCallOrNonVariadicApply(node) {
  20     const callee = astUtils.skipChainExpression(node.callee);
  21
  22     return (
  23         callee.type === "MemberExpression" &&
  24         callee.property.type === "Identifier" &&
  25         callee.computed === false &&
  26         (
  27             (callee.property.name === "call" && node.arguments.length >= 1) ||
  28             (callee.property.name === "apply" && node.arguments.length === 2 && node.arguments[1].type === "ArrayExpression")
  29         )
  30     );
  31 }
  32
  33
  34 /**
  35  * Checks whether or not `thisArg` is not changed by `.call()`/`.apply()`.
  36  * @param {ASTNode|null} expectedThis The node that is the owner of the applied function.
  37  * @param {ASTNode} thisArg The node that is given to the first argument of the `.call()`/`.apply()`.
  38  * @param {SourceCode} sourceCode The ESLint source code object.
  39  * @returns {boolean} Whether or not `thisArg` is not changed by `.call()`/`.apply()`.
  40  */
  41 function isValidThisArg(expectedThis, thisArg, sourceCode) {
  42     if (!expectedThis) {
  43         return astUtils.isNullOrUndefined(thisArg);
  44     }
  45     return astUtils.equalTokens(expectedThis, thisArg, sourceCode);
  46 }
  47
  48 //------------------------------------------------------------------------------
  49 // Rule Definition
  50 //------------------------------------------------------------------------------
  51
  52 /** @type {import('../shared/types').Rule} */
  53 module.exports = {
  54     meta: {
  55         type: "suggestion",
  56
  57         docs: {
  58             description: "disallow unnecessary calls to `.call()` and `.apply()`",
  59             recommended: false,
  60             url: "https://eslint.org/docs/rules/no-useless-call"
  61         },
  62
  63         schema: [],
  64
  65         messages: {
  66             unnecessaryCall: "Unnecessary '.{{name}}()'."
  67         }
  68     },
  69
  70     create(context) {
  71         const sourceCode = context.getSourceCode();
  72
  73         return {
  74             CallExpression(node) {
  75                 if (!isCallOrNonVariadicApply(node)) {
  76                     return;
  77                 }
  78
  79                 const callee = astUtils.skipChainExpression(node.callee);
  80                 const applied = astUtils.skipChainExpression(callee.object);
  81                 const expectedThis = (applied.type === "MemberExpression") ? applied.object : null;
  82                 const thisArg = node.arguments[0];
  83
  84                 if (isValidThisArg(expectedThis, thisArg, sourceCode)) {
  85                     context.report({ node, messageId: "unnecessaryCall", data: { name: callee.property.name } });
  86                 }
  87             }
  88         };
  89     }
  90 };