Partial<> Type

(important) Partial type makes all fields optional on a type. If you have an identical type that requires any of the fields, two types will not be equal to each other in regards to required field

What is it

Constructs a type with all properties of passed type set to optional

• Because all the fields become optional, the new type is considered a subset of the passed type

Using partial will fulfill the type expectation with select fields (hence, the subset)

interface Todo {
  title: string;
  description: string;
}
 
function updateTodo(todo: Todo, fieldsToUpdate: Partial<Todo>) {
  return { ...todo, ...fieldsToUpdate };
}

// full definition
const fullTodo = {
  title: "organize desk",
  description: "clear clutter",
};

// partial definition, leaving out `title` property
const partialTodo = updateTodo(todo1, {
  description: "throw out trash",
});

Use cases

1. using it as a temporary measure on unknown data type
2. not trusting the query to return everything at once

• e.g. not using Prisma type alone, but external type reference

When using a partial, you need a ? on an optional field that is not required in implementation

partialTypedData?.optionalField