Error in TypeScript when compiling Mongoose document middleware

Question

Error in TypeScript when compiling Mongoose document middleware

Problem

After upgrading to TypeScript 3.4, I found that some of my Mongoose middleware functions were failing type checking.

Error Message from TypeScript:

model.ts:19:8 - error TS7017: Element implicitly has an 'any' type because type 'typeof globalThis' has no index signature.

19   this.modified = new Date();

Schema Definition:

Schema.pre("save", next => {
    this.modified = new Date();
    next();
});

Attempts Made to Resolve

Upon using TSLint, it recommended to first cast this to unknown and then cast it to the model type as a workaround.

Schema.pre("update", next => {
    (<Model>(<unknown>this)).modified = new Date();
    next();
});

Although this method seems to work, it is not the most elegant or intuitive solution.

Seeking Suggestions

I am looking for a cleaner way to tackle this issue without having to disable any TypeScript rules. Any suggestions?

typescript mongoose

Answer 1

Answer №1

Hey there, for the most effective solution, refer to this relevant git issue : https://github.com/Automattic/mongoose/issues/5046

The explanation provided in the issue is as follows:

The problem does not stem from Typescript. The issue lies in the usage of fat arrow syntax for defining mongoose methods and hooks. Avoid using fat arrow functions for defining pre-save hooks as they lack lexical scope and cannot be bound to a specific context.

To resolve this, simply replace next => with function(next) {}, and everything should function correctly.

Answer 2

Hey there, for the most effective solution, refer to this relevant git issue : https://github.com/Automattic/mongoose/issues/5046

The explanation provided in the issue is as follows:

The problem does not stem from Typescript. The issue lies in the usage of fat arrow syntax for defining mongoose methods and hooks. Avoid using fat arrow functions for defining pre-save hooks as they lack lexical scope and cannot be bound to a specific context.

To resolve this, simply replace next => with function(next) {}, and everything should function correctly.

Answer 3

Answer №2

Swapping out => with function(next) {} appeared to yield the correct value in this case. However, TypeScript raises an error if attempting to access this.username

Error: TS2339: Property 'username' does not exist on type 'Document'.

To resolve this issue, you have a couple of options. You can either utilize getters and setters such as this.get('username') and this.set('username', 'John'), or implement the following approach:

export interface IUser extends mongoose.Document {
  usernname: string,
  password: string
}

const usersSchema = new mongoose.Schema({
  username: String,
  password: String,
});

usersSchema.pre<IUser>("save", function(next) {
  const user = this;
  // Both user.password and user.username are accessible here.
  next();
});

const User = mongoose.model<IUser>("Users", usersSchema);

Answer 4

Swapping out => with function(next) {} appeared to yield the correct value in this case. However, TypeScript raises an error if attempting to access this.username

Error: TS2339: Property 'username' does not exist on type 'Document'.

To resolve this issue, you have a couple of options. You can either utilize getters and setters such as this.get('username') and this.set('username', 'John'), or implement the following approach:

export interface IUser extends mongoose.Document {
  usernname: string,
  password: string
}

const usersSchema = new mongoose.Schema({
  username: String,
  password: String,
});

usersSchema.pre<IUser>("save", function(next) {
  const user = this;
  // Both user.password and user.username are accessible here.
  next();
});

const User = mongoose.model<IUser>("Users", usersSchema);

Error in TypeScript when compiling Mongoose document middleware

Problem

Attempts Made to Resolve

Seeking Suggestions

Answer №1

Answer №2

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