CODEWITHSUNDEEP
typescript
vmarquet
vmarquet

Reputation: 2532

TypeScript: error TS2322: Type '{}' is not assignable to type '...'

I have an interface:

export default interface ValidationResult {
  valid: boolean
  errors?: string[]
}

And a function that returns an object implementing that interface:

  static validateTitle(title: string): ValidationResult {
    if (title == null || title === '')
      return {valid: false, errors: ["Title can't be empty."]}

    return {valid: true}
  }

But when I try to use the first function inside an other function:

static async validateMovie(title: string): Promise<ValidationResult> {
    const result = this.validateTitle(title)
    if (result.valid === false)
      return new Promise((resolve, reject) => { resolve(result) })
    // other validations...
}

I get a TypeScript error:

error TS2322: Type '{}' is not assignable to type 'ValidationResult'.
  Property 'valid' is missing in type '{}'.

25       return new Promise((resolve, reject) => { resolve(result) })
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I tried casting with as ValidationResult everywhere but without success. What is wrong? I don't understand what TypeScript is complaining about.

Upvotes: 3

Views: 7664

Answers (1)

zerkms
zerkms

Reputation: 255135

Given your function is already async you need just to return result;.

Alternatively you can return new Promise<ValidationResult>.

Typescript does not infer types for promises yet, and it's a known issue: https://github.com/Microsoft/TypeScript/issues/5254

Upvotes: 5

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