Inside the node.js EventEmitter implimentation, the === operator is used within removeListener to determine which listener should be removed. I wanted to test if it remains true to the actual function instance. Here is an example where functions are created in a loop, but each one has a different closure and therefore returns a different result.…

function identity proof.coffee

collector = []

compare = (target) ->
  ->
    console.log 'in timeout, collector length:', collector.length
    for fn, i in collector
      console.log "#{i}:", (fn is target)

for i in [1..3]
  do (i) ->
    foo = -> i
    collector.push foo
    if i is 1
      console.log 'setting timeout'
      setTimeout compare(foo), 20

Conclusion: The comparison function correctly determines that the first function is the one we are referring to. So the identity equality operator is effective at distinguishing between the same function defined in different contexts.