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/**
* @fileoverview Rule to disallow uses of await inside of loops.
* @author Nat Mote (nmote)
*/
"use strict";
/**
* Check whether it should stop traversing ancestors at the given node.
* @param {ASTNode} node A node to check.
* @returns {boolean} `true` if it should stop traversing.
*/
function isBoundary(node) {
const t = node.type;
return (
t === "FunctionDeclaration" ||
t === "FunctionExpression" ||
t === "ArrowFunctionExpression" ||
/*
* Don't report the await expressions on for-await-of loop since it's
* asynchronous iteration intentionally.
*/
(t === "ForOfStatement" && node.await === true)
);
}
/**
* Check whether the given node is in loop.
* @param {ASTNode} node A node to check.
* @param {ASTNode} parent A parent node to check.
* @returns {boolean} `true` if the node is in loop.
*/
function isLooped(node, parent) {
switch (parent.type) {
case "ForStatement":
return (
node === parent.test ||
node === parent.update ||
node === parent.body
);
case "ForOfStatement":
case "ForInStatement":
return node === parent.body;
case "WhileStatement":
case "DoWhileStatement":
return node === parent.test || node === parent.body;
default:
return false;
}
}
module.exports = {
meta: {
type: "problem",
docs: {
description: "disallow `await` inside of loops",
category: "Possible Errors",
recommended: false,
url: "https://eslint.org/docs/rules/no-await-in-loop"
},
schema: [],
messages: {
unexpectedAwait: "Unexpected `await` inside a loop."
}
},
create(context) {
/**
* Validate an await expression.
* @param {ASTNode} awaitNode An AwaitExpression or ForOfStatement node to validate.
* @returns {void}
*/
function validate(awaitNode) {
if (awaitNode.type === "ForOfStatement" && !awaitNode.await) {
return;
}
let node = awaitNode;
let parent = node.parent;
while (parent && !isBoundary(parent)) {
if (isLooped(node, parent)) {
context.report({
node: awaitNode,
messageId: "unexpectedAwait"
});
return;
}
node = parent;
parent = parent.parent;
}
}
return {
AwaitExpression: validate,
ForOfStatement: validate
};
}
};
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