Typescript ignores if statement

Question

let entities: {
  clickPrice: number
} | undefined = Math.random() >= 0.5 ? {
  clickPrice: Math.random()
} : undefined

const clickPrice = Math.random() >= 0.5 ? Math.random() : undefined

type testType = {
  clickPrice: number
}

const test: {
  clickPrice: number
}[] = []

if (entities || clickPrice) {
  test.push({
    clickPrice: entities ? entities.clickPrice : clickPrice
  })
}

Why do I get this error:

Type 'number | undefined' is not assignable to type 'number'.
  Type 'undefined' is not assignable to type 'number'.

on clickPrice

clickPrice: entities ? entities.clickPrice : clickPrice

?
What I want is "If there's entities, or clickPrice, execute some code, which could use only one of them".
TS playground

Jeff Bowman · Accepted Answer · 2021-06-22 17:21:17Z

3

In the section on type narrowing (specifically "control flow analysis"), you can see how TypeScript handles types. In short, TypeScript can narrow entities, and it can narrow clickPrice, but it can't narrow the expression entities || clickPrice in a way that is helpful to you.

You'll have to break it out, at minimal expense to readability:

if (entities) {
  test.push({clickPrice: entities.clickPrice});
} else if (clickPrice) {
  test.push({clickPrice});
}

Playground Link

answered Jun 22, 2021 at 17:21

Jeff Bowman

96.2k19 gold badges227 silver badges266 bronze badges

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

Comments

Vlatko Vlahek · Accepted Answer · 2021-06-22 17:14:08Z

0

Because your type clearly defines this property as number only:

type testType = {
  clickPrice: number
}

However, your code states that if the random number (0-1) is bigger than 0.5, do another random or return undefined if it's not:

const clickPrice = Math.random() >= 0.5 ? Math.random() : undefined

You need to either update the type to support undefined or return a valid number instead.

answered Jun 22, 2021 at 17:14

Vlatko Vlahek

1,88915 silver badges21 bronze badges

2 Comments

sandbox992 Over a year ago

But I push only if there's no undefined - either entities(with required clickPrice), or clickPrice itself. If they're both undefined, code never executes

sandbox992 Over a year ago

Try console.log('test', test) at the end of code block - you'll see, that sometimes it's empty array([])

Alireza Ahmadi · Accepted Answer · 2021-06-22 17:21:13Z

0

You need to use as as number for clickPrice because it might be undefined.

if (entities || clickPrice) {
  test.push({
    clickPrice: entities ? entities.clickPrice : clickPrice as number
  })
}

Here is working one

answered Jun 22, 2021 at 17:21

Alireza Ahmadi

10.2k8 gold badges28 silver badges66 bronze badges

Collectives™ on Stack Overflow

Typescript ignores if statement

3 Answers 3

Comments

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related