Array Product of Other Items in the Array

script.coffee

# Make it a prototype method for Array
Array.prototype.productOthers = ->
    # Set some default values
    [result, total, zeroIndex] = [[], 1, null]

    # Loop through each item in the array
    for num, index in @
        # Set the default value to 0
        result[index] = 0

        # If the number is a 0, handle it
        if num == 0
            # If a zero has been found before, the entire array would be filled with 0s
            if zeroIndex != null
                # If we haven't filled the array yet, fill it before returning
                if result.length != @length
                  while result.length < @length
                    result.push(0)
                return result
                break
            # If this is the first 0, save the index so that we can use it later
            else
                zeroIndex = index
        # Otherwise, multiply the total by the number
        else
             total = total * num

    # If we did find one 0, set the spot where the 0 was found to the product of all other numbers and return
    if zeroIndex != null
        result[zeroIndex] = total
        return result
    # If we didn't find a zero, set the value of each item to the product of all the others (total / item)
    for num, index in @
        result[index] = total / num
    
    return result

firstArray = [0, 1, 0, 3, 7]
secondArray = firstArray.productOthers()

console.log firstArray, secondArray