Multiple Types

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Multiple Types

👨‍💼 Sometimes a value can be one of several types. Union types let you express this.

🐨 Open

index.ts

and:

Create a type ID that is string | number
Implement formatId(id: ID): string — number IDs get a # prefix; string IDs are returned unchanged (including 0 and '')
Create a type Result that is string | Error
Implement processResult(result: Result): string — strings become Success: <value>; Errors become Error: <message>
Export formatId and processResult by name

Completion criteria

Named exports: formatId, processResult
formatId(123) → '#123'; formatId('abc') → 'abc'; formatId(0) → '#0'; formatId('') → ''
processResult('Done!') → 'Success: Done!'
processResult(new Error('Oops')) → 'Error: Oops'

typeof checks if a value is a string, number, boolean, or symbol. For example, typeof value === 'string' returns true if value is a string.

instanceof checks if an object was created from a particular class. For example, value instanceof Error returns true if value is an Error object.