eslint/lib/rules/no-inner-declarations.js

   1 /**
   2  * @fileoverview Rule to enforce declarations in program or function body root.
   3  * @author Brandon Mills
   4  */
   5
   6 "use strict";
   7
   8 //------------------------------------------------------------------------------
   9 // Rule Definition
  10 //------------------------------------------------------------------------------
  11
  12 module.exports = {
  13     meta: {
  14         type: "problem",
  15
  16         docs: {
  17             description: "disallow variable or `function` declarations in nested blocks",
  18             category: "Possible Errors",
  19             recommended: true,
  20             url: "https://eslint.org/docs/rules/no-inner-declarations"
  21         },
  22
  23         schema: [
  24             {
  25                 enum: ["functions", "both"]
  26             }
  27         ],
  28
  29         messages: {
  30             moveDeclToRoot: "Move {{type}} declaration to {{body}} root."
  31         }
  32     },
  33
  34     create(context) {
  35
  36         /**
  37          * Find the nearest Program or Function ancestor node.
  38          * @returns {Object} Ancestor's type and distance from node.
  39          */
  40         function nearestBody() {
  41             const ancestors = context.getAncestors();
  42             let ancestor = ancestors.pop(),
  43                 generation = 1;
  44
  45             while (ancestor && ["Program", "FunctionDeclaration",
  46                 "FunctionExpression", "ArrowFunctionExpression"
  47             ].indexOf(ancestor.type) < 0) {
  48                 generation += 1;
  49                 ancestor = ancestors.pop();
  50             }
  51
  52             return {
  53
  54                 // Type of containing ancestor
  55                 type: ancestor.type,
  56
  57                 // Separation between ancestor and node
  58                 distance: generation
  59             };
  60         }
  61
  62         /**
  63          * Ensure that a given node is at a program or function body's root.
  64          * @param {ASTNode} node Declaration node to check.
  65          * @returns {void}
  66          */
  67         function check(node) {
  68             const body = nearestBody(),
  69                 valid = ((body.type === "Program" && body.distance === 1) ||
  70                     body.distance === 2);
  71
  72             if (!valid) {
  73                 context.report({
  74                     node,
  75                     messageId: "moveDeclToRoot",
  76                     data: {
  77                         type: (node.type === "FunctionDeclaration" ? "function" : "variable"),
  78                         body: (body.type === "Program" ? "program" : "function body")
  79                     }
  80                 });
  81             }
  82         }
  83
  84         return {
  85
  86             FunctionDeclaration: check,
  87             VariableDeclaration(node) {
  88                 if (context.options[0] === "both" && node.kind === "var") {
  89                     check(node);
  90                 }
  91             }
  92
  93         };
  94
  95     }
  96 };