how to find amount of selected items in javascript code example

Example 1: how to find the amount of numbers in a list on python

>>> someList=[]
>>> print len(someList)
0

Example 2: how to make every item compare the rest items of list in python

for i in range(len(mylist)):
    for j in range(i + 1, len(mylist)):
        compare(mylist[i], mylist[j])