This section defines Pipes used for error handling, fallback logic, and safe deep access. These include:

• onError
• lookup
• defaultIfNull
• defaultIfFalsy

onError

• Usage Syntax: {{ inputExpression | onError: fallbackValue }}
• Evaluates to: any
• Description: The onError pipe acts as a catch mechanism: if an error occurs anywhere before this pipe in the expression chain, it replaces the failed result with the provided fallback value.
• • If an error occurs, returns the fallbackValue.
  • If no error occurs, passes through the input value normally.
  • Useful for:
  • • Building safe, fault-tolerant pipelines without throwing user-facing errors.
• Parameters:
• • value:
  • • Type: any
    • Required: Yes
    • Description: The value to substitute if an error occurs.
• Returns:
• • any: The input value if successful; otherwise, the provided fallback value.
• Example 1: Safe fallback for a failing pipe
• • {{ 'not-a-json' | parseJSON | onError: 'Error Message' }}
  • Output: 'Error Message'
• Example 2: No error, normal passthrough
• • {{ 'Hello' | toString | onError: 'Fallback' }}
  • Output: 'Hello'
• Notes:
• • Only catches runtime errors or parsing failures prior to reaching onError.
  • Commonly paired with risky operations like parseJSON, deep mapPath, or dynamic field access.

lookup

• Usage Syntax: {{ inputObject | lookup: 'path': 'to': 'property' }}
• Evaluates to: any
• Description: The lookup pipe navigates through an object and retrieves the value located at the specified path.
• • If the path does not exist, it returns undefined or can be followed by onError to handle missing values.
  • Useful for:
  • • Safely accessing deeply nested properties without chaining multiple checks.
• Parameters:
• • ...path:
  • • Type: string[]
    • Required: Yes
    • Description: A sequence of keys representing the access path.
• Returns:
• • any: The value found at the specified path within the object. If the path does not exist, returns undefined.
• Example 1: Simple object lookup
• • {{ user | lookup: 'name' }}
  • Output: 'Alice' (if user = { name: 'Alice' })
• Example 2: Nested object lookup
• • {{ settings | lookup: 'theme': 'color' }}
  • Output: 'blue' (if settings = { theme: { color: 'blue' } })
• Notes:
• • Each argument in the path corresponds to a nested key in the object.
  • If any key along the path is missing, the lookup short-circuits to undefined.

defaultIfNull

• Usage Syntax: {{ inputValue | defaultIfNull: fallbackValue }}
• Evaluates to: any
• Description: The defaultIfNull pipe checks if the input value is null or undefined and, if so, replaces it with the specified fallback value.
• • Only null and undefined trigger the replacement — other falsy values like 0 or '' are left as-is.
  • Useful for:
  • • Providing defaults without overwriting valid falsy inputs like 0 or an empty string.
• Parameters:
• • value:
  • • Type: any
    • Required: Yes
    • Description: The fallback value if the input is null or undefined.
• Returns:
• • any: The original input if non-nullish; otherwise, the provided fallback value.
• Example 1: Input is null
• • {{ name | defaultIfNull: 'Unknown' }}
  • Output: 'Unknown' (if name = null)
• Example 2: Input is an empty string (not replaced)
• • {{ description | defaultIfNull: 'No description available' }}
  • Output: '' (if description = '')
• Notes:
• • Only null and undefined are considered "nullish" for replacement.
  • Falsy values like 0, false, and '' are kept intact.

defaultIfFalsy

• Usage Syntax: {{ inputValue | defaultIfFalsy: fallbackValue }}
• Evaluates to: any
• Description: The defaultIfFalsy pipe checks if the input is falsy according to JavaScript truthiness rules, and replaces it with the specified fallback value if so.
• • Falsy values include: false, 0, '' (empty string), null, undefined, and NaN.
  • If the input is truthy, it passes through unchanged.
  • Useful for:
  • • Providing guaranteed values when input might be missing, empty, or invalid.
• Parameters:
• • value:
  • • Type: any
    • Required: Yes
    • Description: The fallback value if the input is falsy.
• Returns:
• • any: The input if it is truthy; otherwise, the provided fallback value.
• Example 1: Input is 0 (falsy)
• • {{ quantity | defaultIfFalsy: 1 }}
  • Output: 1 (if quantity = 0)
• Example 2: Input is truthy
• • {{ username | defaultIfFalsy: 'Anonymous' }}
  • Output: 'Alice' (if username = 'Alice')
• Notes:
• • If distinguishing between null/undefined and other falsy values is important, prefer defaultIfNull instead.