the use of an `expected` parameter to mock data values

expected.md

The expected pattern for handling unknown data sources from React's ssr rendering library, in this case a data-attribute value, provides an alternative to event propagation and graceful degradation for error handling.

• is the attribute name safe?
  • if no, return
• does the node have the attribute?
  • if no, return a value of null unless expected is undefined, in which case, return undefined.
• assign the value of getAttribute
• is the value equal to an empty string? return expected
  • otherwise, return the value

This replaces the fault-tolerant pattern of graceful degradation that expects a false value for ambiguous return values with a development environment-friendly data-mocking parameter without the weight of a default.