Prefer not using an async function as a Promise executor JS-0031
Anti-pattern
Major
11 days ago
—
11 days old
Promise executor functions should not be async
75
76// Update client
77ClientSchema.statics.update = (clientId, client, company) => {
78 return new Promise(async (resolve, reject) => { 79 if (company) {
80 var Company = mongoose.model('Company');
81 var query = Company.findOneAndUpdate(Promise executor functions should not be async
36
37// Create client
38ClientSchema.statics.create = (client, company) => {
39 return new Promise(async (resolve, reject) => { 40 if (company) {
41 var Company = mongoose.model('Company');
42 var query = Company.findOneAndUpdate(Promise executor functions should not be async
1166
1167// Delete audit parent
1168AuditSchema.statics.deleteParent = (isAdmin, auditId, userId) => {
1169 return new Promise(async (resolve, reject) => {1170 var query = Audit.findByIdAndUpdate(auditId, { parentId: null });
1171 if (!isAdmin) query.or([{ creator: userId }, { collaborators: userId }]);
1172 queryPromise executor functions should not be async
1144
1145// Update audit parent
1146AuditSchema.statics.updateParent = (isAdmin, auditId, userId, parentId) => {
1147 return new Promise(async (resolve, reject) => {1148 var query = Audit.findByIdAndUpdate(auditId, { parentId: parentId });
1149 if (!isAdmin) query.or([{ creator: userId }, { collaborators: userId }]);
1150 queryPromise executor functions should not be async
1111 });
1112
1113AuditSchema.statics.updateApprovals = (isAdmin, auditId, userId, update) => {
1114 return new Promise(async (resolve, reject) => {1115 var Settings = mongoose.model('Settings');
1116 var settings = await Settings.getAll();
1117
Description
The new Promise constructor accepts an executor function as an argument, which has resolve and reject parameters that can be used to control the state of the created Promise.
For example:
const result = new Promise(function executor(resolve, reject) {
readFile('foo.txt', (err, result) => {
if (err) {
reject(err);
} else {
resolve(result);
}
});
});
The executor function can also be an async function.
However, this is usually a mistake, for a few reasons:
- The
Promiseconstructor can only catch synchronous exceptions, and an async function never throws - it always returns a promise (which might get rejected though). And that return value is ignored, as the promise is waiting for resolve to be called. - Therefore, if an async executor function throws an error, the error will be lost and won't cause the newly-constructed
Promiseto reject. This could make it difficult to debug and handle some errors. - If a Promise executor function is using
await, this is usually a sign that it is not actually necessary to use the new Promise constructor, or the scope of thenew Promiseconstructor can be reduced.
Bad Practice
const foo = new Promise(async (resolve, reject) => {
readFile('foo.txt', (err, result) => {
if (err) {
reject(err);
} else {
resolve(result);
}
});
});
const result = new Promise(async (resolve, reject) => {
resolve(await foo);
});
Recommended
const foo = new Promise((resolve, reject) => {
readFile('foo.txt', function(err, result) {
if (err) {
reject(err);
} else {
resolve(result);
}
});
});
const result = Promise.resolve(foo);