Snippet to recursively search a JSON structure for a leaf value - returns the path

find_value.coffee

find_value = (haystack, needle, cache=new WeakMap()) ->

  # console.log "haystack: ", haystack 
  # console.log "needle: ", needle

  try 
    if haystack?
      unless typeof haystack == 'object' and cache.has haystack 
        cache.set haystack, true 
        for key, value of haystack 
          if value == needle
            return key 
          else 
            if typeof value == 'object'
              found = find_value value, needle, cache 
              if found?
                return "#{key}.#{found}"
        return null 
  catch err 
    console.error typeof haystack, haystack 
    console.error typeof needle, needle 
    console.error err 
  return null 

foo = 
  baz: 
    bang: 'blah'

 console.log foo 
 console.log find_value foo, 'blah'

Yields:

{ baz: { bang: 'blah' } }
object:  { baz: { bang: 'blah' } }
needle:  blah
object:  { bang: 'blah' }
needle:  blah
baz.bang