Difference between .exec() and .execPopulate() in Mongoose?

Here I answer what is the difference between .exec() and .execPopulate() in Mongoose?

1. .exec() is used with a query while .execPopulate() is used with a document

Syntax for .exec() is as follows:

Model.query()
  .populate('field')
  .exec() // returns promise
  .then(function (document) {
    console.log(document);
  });

Syntax for .execPopulate() is as follows:

fetchedDocument
  .populate('field')
  .execPopulate() // returns promise
  .then(function (document) {
    console.log(document);
  });

When working with individual document use .execPopulate(), for model query use .exec(). Both returns a promise. One can do without .exec() or .execPopulate() but then has to pass a callback in populate.