scientific notation

I used division operator and tests failed for big numbers. I don't understand why

It is so amazing to see a short solution

I thought the same thing about my solution. We know which is more readable, but which is faster?

It is after you explain that I could understand it. THX as well.

Please, do use the spoiler flag when you post comment (even here: comments about solutions are visible in the dashboard by anyone) with indications about the solution. I did flag your message.

In JavaScript, .join() is an Array method, not a String method.

["foo", "bar"].join('');    // "foobar"
"foo".join("bar");          // VM910:2 Uncaught TypeError: "foo".join is not a function(…)

To put two strings together, you would use the .concat() method, or use the "+" operator.

"foo".concat("bar");        // "foobar"
"foo" + "bar";              // "foobar"