The input type 'unknown' cannot be assigned to the output type 'string' when utilizing the filter(Boolean) operator

Question

The input type 'unknown' cannot be assigned to the output type 'string' when utilizing the filter(Boolean) operator

.ts:

siteName: string;

    this.store.pipe(
          select(getSiteName),
          filter(Boolean),
          take(1)
        ).subscribe(siteName => this.siteName = siteName);

Error:

Type 'unknown' is not assignable to type 'string'

I encountered the error message mentioned above for the variable this.siteName after including the filter(Boolean) operator in the pipe. Strangely, no errors were present prior to adding the filter operator. Any ideas on what might be causing this issue?

angular typescript

Answer 1

Answer №1

The issue arises because TypeScript does not support using the Boolean constructor as the predicate function for the filter method. To resolve this, you can use an explicit predicate function instead, like so:

this.store.pipe(
    select(getSiteName),
    filter(x => Boolean(x)),
    take(1)
).subscribe(siteName => this.siteName = siteName);

Answer 2

The issue arises because TypeScript does not support using the Boolean constructor as the predicate function for the filter method. To resolve this, you can use an explicit predicate function instead, like so:

this.store.pipe(
    select(getSiteName),
    filter(x => Boolean(x)),
    take(1)
).subscribe(siteName => this.siteName = siteName);

Answer 3

Answer №2

It seems like the issue lies in the parameter of the subscribe function not having a specified type.

.subscribe(siteName => this.siteName = siteName);

A more accurate approach would be:

.subscribe(siteName:string => this.siteName = siteName);

Answer 4

It seems like the issue lies in the parameter of the subscribe function not having a specified type.

.subscribe(siteName => this.siteName = siteName);

A more accurate approach would be:

.subscribe(siteName:string => this.siteName = siteName);

The input type 'unknown' cannot be assigned to the output type 'string' when utilizing the filter(Boolean) operator

Answer №1

Answer №2

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