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/**
* @fileoverview Rule to disallow uses of await inside of loops.
* @author Nat Mote (nmote)
*/
"use strict";
// Node types which are considered loops.
const loopTypes = new Set([
"ForStatement",
"ForOfStatement",
"ForInStatement",
"WhileStatement",
"DoWhileStatement"
]);
/*
* Node types at which we should stop looking for loops. For example, it is fine to declare an async
* function within a loop, and use await inside of that.
*/
const boundaryTypes = new Set([
"FunctionDeclaration",
"FunctionExpression",
"ArrowFunctionExpression"
]);
module.exports = {
meta: {
docs: {
description: "disallow `await` inside of loops",
category: "Possible Errors",
recommended: false,
url: "https://eslint.org/docs/rules/no-await-in-loop"
},
schema: []
},
create(context) {
return {
AwaitExpression(node) {
const ancestors = context.getAncestors();
// Reverse so that we can traverse from the deepest node upwards.
ancestors.reverse();
/*
* Create a set of all the ancestors plus this node so that we can check
* if this use of await appears in the body of the loop as opposed to
* the right-hand side of a for...of, for example.
*/
const ancestorSet = new Set(ancestors).add(node);
for (let i = 0; i < ancestors.length; i++) {
const ancestor = ancestors[i];
if (boundaryTypes.has(ancestor.type)) {
/*
* Short-circuit out if we encounter a boundary type. Loops above
* this do not matter.
*/
return;
}
if (loopTypes.has(ancestor.type)) {
/*
* Only report if we are actually in the body or another part that gets executed on
* every iteration.
*/
if (
ancestorSet.has(ancestor.body) ||
ancestorSet.has(ancestor.test) ||
ancestorSet.has(ancestor.update)
) {
context.report({
node,
message: "Unexpected `await` inside a loop."
});
return;
}
}
}
}
};
}
};
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