He calls the replace(). Replace accepts something called a regex (which tells your replace method to expect a certain type of string pattern -- in this case the regex is a '.' which ensures your input is any character but a line terminator). The second parameter replace accepts is a callback function. The callback function contains a dictionary of matching DNA values. This function runs on each individual character from the original dna string and 'replaces' it with the matching DNA value from the dictionary.

Modification done.

OK! Sorry:-( I forgot that I modified the TS solution; at first my result was like yours.
Anyway as soon as I can I will modify the testing function so that different solutions could occur. I will let you know when done.
Thanks for your post.

In expected 105 is greater than your 104. You should try to return at each step the greatest number.
The description says:

decompose(11) must return [1,2,4,10]. Note that there are actually two ways to decompose 11², 11² = 121 = 1 + 4 + 16 + 100 = 1² + 2² + 4² + 10² but don't return [2,6,9], since 9 is smaller than 10.