Add type narrowing for error checks (#103)

lp247 · web-flow · commit 92877529f748 · 2025-08-20T11:27:39.000+02:00
This change enables type narrowing for the static functions
GenericError.isGenericError, MultipleErrors.isGenericErrors, and
MultipleErrors.isGenericError.
diff --git a/src/errors.ts b/src/errors.ts
@@ -31,7 +31,7 @@ export class GenericError extends Error {
   [index: string]: any
   [kGenericError]: true
 
-  static isGenericError (error: Error): boolean {
+  static isGenericError (error: Error): error is GenericError | MultipleErrors {
     return (error as GenericError)[kGenericError] === true
   }
 
@@ -71,11 +71,11 @@ export class MultipleErrors extends AggregateError {
 
   static code: ErrorCode = 'PLT_KFK_MULTIPLE'
 
-  static isGenericError (error: Error): boolean {
+  static isGenericError (error: Error): error is GenericError | MultipleErrors {
     return (error as GenericError)[kGenericError] === true
   }
 
-  static isMultipleErrors (error: Error): boolean {
+  static isMultipleErrors (error: Error): error is MultipleErrors {
     return (error as MultipleErrors)[kMultipleErrors] === true
   }
 

Original file line number	Diff line number	Diff line change
`@@ -31,7 +31,7 @@ export class GenericError extends Error {`
`31`	`31`	`[index: string]: any`
`32`	`32`	`[kGenericError]: true`
`33`	`33`
`34`		`- static isGenericError (error: Error): boolean {`
	`34`	`+ static isGenericError (error: Error): error is GenericError \| MultipleErrors {`
`35`	`35`	`return (error as GenericError)[kGenericError] === true`
`36`	`36`	`}`
`37`	`37`
`@@ -71,11 +71,11 @@ export class MultipleErrors extends AggregateError {`
`71`	`71`
`72`	`72`	`static code: ErrorCode = 'PLT_KFK_MULTIPLE'`
`73`	`73`
`74`		`- static isGenericError (error: Error): boolean {`
	`74`	`+ static isGenericError (error: Error): error is GenericError \| MultipleErrors {`
`75`	`75`	`return (error as GenericError)[kGenericError] === true`
`76`	`76`	`}`
`77`	`77`
`78`		`- static isMultipleErrors (error: Error): boolean {`
	`78`	`+ static isMultipleErrors (error: Error): error is MultipleErrors {`
`79`	`79`	`return (error as MultipleErrors)[kMultipleErrors] === true`
`80`	`80`	`}`
`81`	`81`