TypeScript Expected 1 arguments, but got 2.'

Question

I have an object property with the following signature.

handleItem = (data: Output & { isValid: boolean }) => {}

I do not understand the & part.

Basically I trying to pass some arguments as:

handleItem (outputItem, { isValid: false })

and I receive an error

Expected 1 arguments, but got 2.'

How to pass values property? How the & is used in this instance?

It looks like `& { isValid: boolean }` is describing the `data: Output` part. This makes sense, considering there should be one argument. — Feathercrown, Feb 02 '18 at 13:39
Everything after the `:` is a type annotation. The function only takes a single object as argument. (And that object needs to contain an `isValid` property.) — deceze, Feb 02 '18 at 13:39
handleItem = (data: Output, obj: { isValid: boolean }) => {} — Lyubimov Roman, Feb 02 '18 at 13:40
not sure ,could you please provide me an example how to call this one? — Radex, Feb 02 '18 at 13:41

Titian Cernicova-Dragomir · Accepted Answer · 2018-02-02T13:44:03.160

6

handleItem takes a single argument, an object that has the properties of Output and the isValid property. You need to construct such an object. Using the spread operator is a good option:

handleItem ({ isValid: false, ...outputItem })

You can read more about intersection types here

edited Feb 02 '18 at 13:44

answered Feb 02 '18 at 13:42

Titian Cernicova-Dragomir

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this one does the trick thanks – Radex Feb 02 '18 at 13:43

messerbill · Answer 2 · 2018-02-02T13:49:40.323

this is called Intersection Type and it means that your param of your handleItem() method combines Output and { isValid: boolean } - will say that your parameter needs to have both types, Output and { isValid: boolean }.

Typescript & operator

so you need to call it this way:

handleItem ({ isValid: false, ...outputItem })

if you want to pass two parameters do the following:

handleItem = (data: Output, { isValid: boolean }) => {}

afterwards you can do:

handleItem (outputItem, { isValid: false })

score 2 · Answer 3 · answered Feb 02 '18 at 13:42

& is a type intersection. Output & { isValid: boolean } means it expects something as argument that conforms both to the interface Output and { isValid: boolean }. In other words, it expects one object which has an isValid property and whatever else Output defines.

score 0 · Answer 4 · answered Feb 02 '18 at 13:41

0

I think the syntax expect the property isValid of data to be boolean

answered Feb 02 '18 at 13:41

Faly

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TypeScript Expected 1 arguments, but got 2.'

4 Answers4