Space1000

The reducer function takes four arguments:

Accumulator (acc)
Current Value (cur)
Current Index (idx)
Source Array (src)

a = [1,2,3]

result = [9].concat(a).reduce (acc,el) -> 
  console.dir arguments
  acc + cur

console.dir result

array
  .reduce ((acc,cur,idx,src) -> return acc + cur), 0