Comparison between a Typescript optional field and a field that has the potential to be undefined

Question

Can you clarify the contrast between an optional field and a T | undefined field?

export interface Example {
  property1: string | undefined
  property2?: string
}

Answer 1

Answer №1

Including an optional field in your object initialization with type Demo is not mandatory.

In Scenario A, field1 is a union type, allowing it to hold either a value of type string or undefined.

export interface Demo {
  field1: string | undefined;
}

When creating an object of type Demo, you must specify the property field1 with its defined type from the interface.

demo: Demo = {
  field1: undefined
}

On the other hand, Scenario B involves field2 as an optional property,

export interface Demo {
  field2?: string;
}

It is not necessary to include the property field2 when defining an object of type Demo.

demo: Demo = {}

Answer 2

Including an optional field in your object initialization with type Demo is not mandatory.

In Scenario A, field1 is a union type, allowing it to hold either a value of type string or undefined.

export interface Demo {
  field1: string | undefined;
}

When creating an object of type Demo, you must specify the property field1 with its defined type from the interface.

demo: Demo = {
  field1: undefined
}

On the other hand, Scenario B involves field2 as an optional property,

export interface Demo {
  field2?: string;
}

It is not necessary to include the property field2 when defining an object of type Demo.

demo: Demo = {}