Error when initializing constant with 'this' | 'this' implicitly has type 'any' because it does not have a type annotation

Question

I have a file 'test.js' and I changed it's extension to .ts. What I'm really trying to do is to slowly migrate a .js codebase to typescript.

Now I'm getting the following error:

'this' implicitly has type 'any' because it does not have a type annotation.

This is the code:

animalSchema.pre('save', function save(next) {
  const animal = this;
  if (!animal.isModified('id')) {
    return next();
  }
  animal.name = "Test Animal";
  next();
  });
});

And this is my tsconfig.js:

{
  "compilerOptions": {
    "target": "es5",
    "module": "commonjs",
    "allowJs": true,
    "sourceMap": true,
    "outDir": "./build",
    "rootDir": "./src",
    "strict": false,
    "noImplicitAny": false,
    "noImplicitThis": false,
    "moduleResolution": "node",
    "esModuleInterop": true
  }
}