@jclem/get-in v2.0.1

getIn

This package provides a function getIn, which allows null-error and type-safe traversal of objects.

The getIn function works by wrapping a value in a function that returns that value, and then wrapping that function in a Proxy. To use it, call getIn on the object you want to traverse (e.g. getIn(object)) and get properties as you normally would, but when you want an actual value, call the property like a function (e.g. getIn(object).foo.bar[0][1].baz()). The return value will be null or the value itself.

Limitations

• There are likely edge cases here. I've mostly experimented with simple arrays and plain JavaScript objects.
• Even if a type is non-nullable (such as firstName in the below example), the type will be nullable when gotten through getIn, and you'll need to perform a check for the type checker to be happy. I haven't found a way around this, yet.

Example

type Person = {
  firstName: string
  middleName?: string
  lastName: string
  
  address?: Address
}

type Address = {
  streets: string[]
  city: string
  state: string
  zip: string
}

const p1: Person = {
  firstName: 'Jonathan',
  lastName: 'Clem',
  
  address: {
    streets: ['123 Main St.'],
    city: 'Juneau',
    state: 'Alaska',
    zip: '11111'
  }
}

const p2: Person = {
  firstName: 'Bob',
  lastName: 'Clem'
}

getIn(p1).firstName() // Type is string | null
getIn(p1).address.state() // Type is string | null, value is `'Alaska'`.
getIn(p1).address.streets[0]() // Type is string | null, value is `'123 Main St.'`.
getIn(p2).address.streets[1]() // Type is string | null, value is `null`.