From binary to a number

Problem

In binary there are only zeros and ones, and every position is worth twice as much as the one to its right: 1, 2, 4, 8, 16, 32...

Write a function that takes a string of zeros and ones and returns the number it stands for. With "1010" the answer is 10, because it is 8 + 0 + 2 + 0.

There is a comfortable road: go through the string from left to right and, on each character, double what you have so far and add 1 if that character is a one. When the string ends you already have the number.

Leading zeros are harmless: "0011" is 3 as well.

If the string holds anything else (a 2, a letter, a space) it is not a binary number: in that case you return -1. The empty string is not a number either, so it returns -1 too.

Examples

• The one from the example

  "1010" → 10

• A single one

  "1" → 1

• Two ones make three

  "11" → 3

• Five digits

  "11010" → 26

• A long one

  "10001101000" → 1128

• Leading zeros

  "00011111" → 31

• A digit sneaked in the middle

  "1021" → -1

• Letters stuck at the end

  "10cats" → -1

• A space in the middle

  "101 010" → -1

Besides these, the challenge has hidden tests that are revealed when you submit your solution.

You start with this

def binary_to_number(text):
    pass

function binaryToNumber(text) {
}