Kayode Oluwasegun
Kayode Oluwasegun

Kayode Oluwasegun

Making the Properties of an Object Optional in Typescript

Making the Properties of an Object Optional in Typescript

Kayode Oluwasegun's photo
Kayode Oluwasegun
·Jul 4, 2022·

1 min read

In cases where you want to construct a type with all properties of another type set to optional, the Partial<Type> is a helpful utility.

This is pretty useful when you need the subset of a given type.

For instance,

interface Person {
  name: string;
  age: number;
}

let persons: Person[] = [
  { name: "Abel", age: 19 },
  { name: "Drake", age: 23 },
  { name: "Lucid", age: 22 },
  { name: "Mark", age: 87 },
];

// takes an argument of 
function searchBySub(subObj: Partial<Person>) {
  return persons.find((person) => {
    return Object.keys(subObj).every((key) => {
      return person[key] === subObj[key];
    });
  });
}

The argument, subOj, can only be a sub-type of Person, so the code below would raise a type error

searchBySub({ unknownProperty: "unknown" }) 
// error - Argument of type '{ unknownProperty: string }' is not
// assignable to parameter of type 'Partial<Person>'
 
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