How to loop through object fields in TypeScript

Question

I want to avoid doing this:

handleUserChange?.({ target: { name: 'first_name', value: rentalOrder?.address?.first_name } })
handleUserChange?.({ target: { name: 'last_name', value: rentalOrder?.address?.last_name } })
handleUserChange?.({ target: { name: 'address_line_one', value: rentalOrder?.address?.address_line_one } })

So instead I have:

const fieldsFromDeliveryAddress = ['first_name', 'last_name', 'address_line_one', 'post_code', 'city', 'phone']
fieldsFromDeliveryAddress.forEach(fieldName => handleUserChange?.({ target: { name: fieldName, value: rentalOrder?.address?.[fieldName] } }))

But it gives me the TypeScript error (on line 2, rentalOrder?.address?.[fieldName] is underlined in red):

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ first_name: string; last_name: string; email?: string | undefined; address_line_one: string; address_line_two?: string | undefined; country: string; city: string; post_code: string; phone: string; }'.

No index signature with a parameter of type 'string' was found on type '{ first_name: string; last_name: string; email?: string | undefined; address_line_one: string; address_line_two?: string | undefined; country: string; city: string; post_code: string; phone: string; }'

How can I solve this?

Update

Function signatures:

const handleUserChange = ({ target }: HTMLSimpleElementEvent): void

interface HTMLSimpleElementEvent {
  target: {
    name: string
    type?: string
    value?: any
    checked?: boolean
  }
}

What's the type signature of handleUserChange? On what line do you get this error? — ShamPooSham
– ShamPooSham, Commented Apr 1, 2022 at 9:16
Try to do const fieldsFromDeliveryAddress = ['first_name', 'last_name', 'address_line_one', 'post_code', 'city', 'phone'] as const. Does that work? — ShamPooSham
– ShamPooSham, Commented Apr 1, 2022 at 10:19

Антон Невзгодов · Accepted Answer · 2022-04-01 11:12:42Z

1

You need to add as const. Typescript will treat your array as a tuple and you'll have proper types for your forEach callback.

const fieldsFromDeliveryAddress = ['first_name', 'last_name', 'address_line_one', 'post_code', 'city', 'phone'] as const;
fieldsFromDeliveryAddress.forEach(fieldName => handleUserChange?.({ target: { name: fieldName, value: rentalOrder?.address?.[fieldName] } }))

answered Apr 1, 2022 at 11:12

Антон Невзгодов

3591 silver badge6 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to loop through object fields in TypeScript

Update

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

Update

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related