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javascriptcoffeescriptconstantsformbuilder

What's the advantage of mapping a JavaScript string to a "constant"?

Looking through the Department of Better Technology's Formbuilder library, I see several cases of strings mapped to capital-letter object properties, as if imitating constants in JavaScript. The following is in main.coffee:

mappings:
      SIZE: 'field_options.size'
      UNITS: 'field_options.units'
      LABEL: 'label'
      FIELD_TYPE: 'field_type'
      ...

These "constants" are then mostly interpolated in strings that make up views. From paragraph.coffee:

view: """
    <textarea class='rf-size-<%= rf.get(Formbuilder.options.mappings.SIZE) %>'></textarea>
  """

Is there a performance or architectural advantage in doing this, aside from not having to use literals? Seems like it would be less painstaking, if not faster, just to use the string.

Solution

  • Poor man's declaration safety.

    rf.get('field_optons.size')
// => undefined (I assume, depends on rf.get)
rf.get(Formbuilder.optons.mappings.SIZE)
// => TypeError: Cannot read property 'mappings' of undefined

    A typo in the first case lets your code proceed with a wrong value (undefined).

    A typo in the second case, unless it is in the last component, will abort your program.