eslint/lib/rules/no-await-in-loop.js

   1 /**
   2  * @fileoverview Rule to disallow uses of await inside of loops.
   3  * @author Nat Mote (nmote)
   4  */
   5 "use strict";
   6
   7 /**
   8  * Check whether it should stop traversing ancestors at the given node.
   9  * @param {ASTNode} node A node to check.
  10  * @returns {boolean} `true` if it should stop traversing.
  11  */
  12 function isBoundary(node) {
  13     const t = node.type;
  14
  15     return (
  16         t === "FunctionDeclaration" ||
  17         t === "FunctionExpression" ||
  18         t === "ArrowFunctionExpression" ||
  19
  20         /*
  21          * Don't report the await expressions on for-await-of loop since it's
  22          * asynchronous iteration intentionally.
  23          */
  24         (t === "ForOfStatement" && node.await === true)
  25     );
  26 }
  27
  28 /**
  29  * Check whether the given node is in loop.
  30  * @param {ASTNode} node A node to check.
  31  * @param {ASTNode} parent A parent node to check.
  32  * @returns {boolean} `true` if the node is in loop.
  33  */
  34 function isLooped(node, parent) {
  35     switch (parent.type) {
  36         case "ForStatement":
  37             return (
  38                 node === parent.test ||
  39                 node === parent.update ||
  40                 node === parent.body
  41             );
  42
  43         case "ForOfStatement":
  44         case "ForInStatement":
  45             return node === parent.body;
  46
  47         case "WhileStatement":
  48         case "DoWhileStatement":
  49             return node === parent.test || node === parent.body;
  50
  51         default:
  52             return false;
  53     }
  54 }
  55
  56 module.exports = {
  57     meta: {
  58         type: "problem",
  59
  60         docs: {
  61             description: "disallow `await` inside of loops",
  62             recommended: false,
  63             url: "https://eslint.org/docs/rules/no-await-in-loop"
  64         },
  65
  66         schema: [],
  67
  68         messages: {
  69             unexpectedAwait: "Unexpected `await` inside a loop."
  70         }
  71     },
  72     create(context) {
  73
  74         /**
  75          * Validate an await expression.
  76          * @param {ASTNode} awaitNode An AwaitExpression or ForOfStatement node to validate.
  77          * @returns {void}
  78          */
  79         function validate(awaitNode) {
  80             if (awaitNode.type === "ForOfStatement" && !awaitNode.await) {
  81                 return;
  82             }
  83
  84             let node = awaitNode;
  85             let parent = node.parent;
  86
  87             while (parent && !isBoundary(parent)) {
  88                 if (isLooped(node, parent)) {
  89                     context.report({
  90                         node: awaitNode,
  91                         messageId: "unexpectedAwait"
  92                     });
  93                     return;
  94                 }
  95                 node = parent;
  96                 parent = parent.parent;
  97             }
  98         }
  99
 100         return {
 101             AwaitExpression: validate,
 102             ForOfStatement: validate
 103         };
 104     }
 105 };