Mongoose method scope in TypeScript

Question

I have a question about the scope of the object in the callback function of Mongoose methods. My employee has 'addresses'. When you call this 'method' it looks for the addresses in the addresses model.

Javascript:

employeeSchema.methods.getAddresses = function (callback) { 
  addressModel.find({ _id: { $in: this.addresses } }, function (err, obj) {
    callback(obj);
  });
};

I want to make everything typed and have an issue with the 'this' scope in the function. The scope is on the object itself, however all examples show 'this'. This won't work in TypeScript as it thinks it is the main class.

TypeScript:

employeeSchema.methods.getAddresses = (callback) => { 
  addressModel.find({ _id: { $in: this.addresses } }, (err, obj) => {
    callback(obj);
  });
};

I have the same issue with validation:

accountSchema.path('email').validate(function (email, callback) {
  if (this.isNew || this.isModified('email')) {}
}

'This' is the account in the scope of the callback, but is there a way to actually pass the object to the callback?

Why not just pass in addresses into your method as a parameter? (addresses, callback)...then the caller will use "this.addresses" — Arthur Frankel
– Arthur Frankel, Commented Sep 29, 2014 at 14:44

basarat · Accepted Answer · 2014-09-29 23:32:12Z

1

Since you don't want to capture the lexically scoped this, don't use =>. Just use function.

There is a feature request to declare the meaning of this to be a particular type: https://github.com/Microsoft/TypeScript/issues/229

answered Sep 29, 2014 at 23:32

basarat

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2 Comments

user3644852 Over a year ago

Oke I will use function() and cast this to the typed object until then. Thanks

basarat Over a year ago

just a tip : prefer the term assert instead of cast as there isn't any runtime support

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