eslint/lib/rules/prefer-rest-params.js

   1 /**
   2  * @fileoverview Rule to
   3  * @author Toru Nagashima
   4  */
   5
   6 "use strict";
   7
   8 //------------------------------------------------------------------------------
   9 // Helpers
  10 //------------------------------------------------------------------------------
  11
  12 /**
  13  * Gets the variable object of `arguments` which is defined implicitly.
  14  * @param {eslint-scope.Scope} scope A scope to get.
  15  * @returns {eslint-scope.Variable} The found variable object.
  16  */
  17 function getVariableOfArguments(scope) {
  18     const variables = scope.variables;
  19
  20     for (let i = 0; i < variables.length; ++i) {
  21         const variable = variables[i];
  22
  23         if (variable.name === "arguments") {
  24
  25             /*
  26              * If there was a parameter which is named "arguments", the implicit "arguments" is not defined.
  27              * So does fast return with null.
  28              */
  29             return (variable.identifiers.length === 0) ? variable : null;
  30         }
  31     }
  32
  33     /* istanbul ignore next : unreachable */
  34     return null;
  35 }
  36
  37 /**
  38  * Checks if the given reference is not normal member access.
  39  *
  40  * - arguments         .... true    // not member access
  41  * - arguments[i]      .... true    // computed member access
  42  * - arguments[0]      .... true    // computed member access
  43  * - arguments.length  .... false   // normal member access
  44  * @param {eslint-scope.Reference} reference The reference to check.
  45  * @returns {boolean} `true` if the reference is not normal member access.
  46  */
  47 function isNotNormalMemberAccess(reference) {
  48     const id = reference.identifier;
  49     const parent = id.parent;
  50
  51     return !(
  52         parent.type === "MemberExpression" &&
  53         parent.object === id &&
  54         !parent.computed
  55     );
  56 }
  57
  58 //------------------------------------------------------------------------------
  59 // Rule Definition
  60 //------------------------------------------------------------------------------
  61
  62 module.exports = {
  63     meta: {
  64         type: "suggestion",
  65
  66         docs: {
  67             description: "require rest parameters instead of `arguments`",
  68             recommended: false,
  69             url: "https://eslint.org/docs/rules/prefer-rest-params"
  70         },
  71
  72         schema: [],
  73
  74         messages: {
  75             preferRestParams: "Use the rest parameters instead of 'arguments'."
  76         }
  77     },
  78
  79     create(context) {
  80
  81         /**
  82          * Reports a given reference.
  83          * @param {eslint-scope.Reference} reference A reference to report.
  84          * @returns {void}
  85          */
  86         function report(reference) {
  87             context.report({
  88                 node: reference.identifier,
  89                 loc: reference.identifier.loc,
  90                 messageId: "preferRestParams"
  91             });
  92         }
  93
  94         /**
  95          * Reports references of the implicit `arguments` variable if exist.
  96          * @returns {void}
  97          */
  98         function checkForArguments() {
  99             const argumentsVar = getVariableOfArguments(context.getScope());
 100
 101             if (argumentsVar) {
 102                 argumentsVar
 103                     .references
 104                     .filter(isNotNormalMemberAccess)
 105                     .forEach(report);
 106             }
 107         }
 108
 109         return {
 110             "FunctionDeclaration:exit": checkForArguments,
 111             "FunctionExpression:exit": checkForArguments
 112         };
 113     }
 114 };