fix(errors): made sure extend errors are named and inherited properly

lib/errors.spec.ts

@@ -0,0 +1,22 @@
+import { DuplicateError, DuplicateConstraintError } from './errors'
+
+describe( 'errors', ( ) =>
+{
+	describe( 'DuplicateError', ( ) =>
+	{
+		it( 'should have proper name', ( ) =>
+		{
+			const err = new DuplicateError( "err" );
+			expect( err.name ).toBe( "DuplicateError" );
+		} );
+	} );
+
+	describe( 'DuplicateConstraintError', ( ) =>
+	{
+		it( 'should have proper name', ( ) =>
+		{
+			const err = new DuplicateConstraintError( "err" );
+			expect( err.name ).toBe( "DuplicateConstraintError" );
+		} );
+	} );
+} );

lib/errors.ts

@@ -1,11 +1,20 @@
 
 export class DuplicateError extends Error
-{ }
+{
+	constructor( message?: string )
+	{
+		super( message );
+		Object.setPrototypeOf( this, DuplicateError.prototype );
+		this.name = this.constructor.name;
+	}
+}
 
 export class DuplicateConstraintError extends DuplicateError
 {
 	constructor( field: string )
 	{
 		super( `Constraint ${field} already set.` );
+		Object.setPrototypeOf( this, DuplicateConstraintError.prototype );
+		this.name = this.constructor.name;
 	}
 }