eslint/lib/rules/prefer-spread.js

   1 /**
   2  * @fileoverview A rule to suggest using of the spread operator instead of `.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 `.apply()` for variadic.
  16  * @param {ASTNode} node A CallExpression node to check.
  17  * @returns {boolean} Whether or not the node is a `.apply()` for variadic.
  18  */
  19 function isVariadicApplyCalling(node) {
  20     return (
  21         astUtils.isSpecificMemberAccess(node.callee, null, "apply") &&
  22         node.arguments.length === 2 &&
  23         node.arguments[1].type !== "ArrayExpression" &&
  24         node.arguments[1].type !== "SpreadElement"
  25     );
  26 }
  27
  28 /**
  29  * Checks whether or not `thisArg` is not changed by `.apply()`.
  30  * @param {ASTNode|null} expectedThis The node that is the owner of the applied function.
  31  * @param {ASTNode} thisArg The node that is given to the first argument of the `.apply()`.
  32  * @param {RuleContext} context The ESLint rule context object.
  33  * @returns {boolean} Whether or not `thisArg` is not changed by `.apply()`.
  34  */
  35 function isValidThisArg(expectedThis, thisArg, context) {
  36     if (!expectedThis) {
  37         return astUtils.isNullOrUndefined(thisArg);
  38     }
  39     return astUtils.equalTokens(expectedThis, thisArg, context);
  40 }
  41
  42 //------------------------------------------------------------------------------
  43 // Rule Definition
  44 //------------------------------------------------------------------------------
  45
  46 /** @type {import('../shared/types').Rule} */
  47 module.exports = {
  48     meta: {
  49         type: "suggestion",
  50
  51         docs: {
  52             description: "Require spread operators instead of `.apply()`",
  53             recommended: false,
  54             url: "https://eslint.org/docs/latest/rules/prefer-spread"
  55         },
  56
  57         schema: [],
  58         fixable: null,
  59
  60         messages: {
  61             preferSpread: "Use the spread operator instead of '.apply()'."
  62         }
  63     },
  64
  65     create(context) {
  66         const sourceCode = context.sourceCode;
  67
  68         return {
  69             CallExpression(node) {
  70                 if (!isVariadicApplyCalling(node)) {
  71                     return;
  72                 }
  73
  74                 const applied = astUtils.skipChainExpression(astUtils.skipChainExpression(node.callee).object);
  75                 const expectedThis = (applied.type === "MemberExpression") ? applied.object : null;
  76                 const thisArg = node.arguments[0];
  77
  78                 if (isValidThisArg(expectedThis, thisArg, sourceCode)) {
  79                     context.report({
  80                         node,
  81                         messageId: "preferSpread"
  82                     });
  83                 }
  84             }
  85         };
  86     }
  87 };