When slicing a string with a simple start, stop range, it fails to render, throwing a join error.

new SliceString('hello')[[1,3]]; // Fails

Looking at the code, it looks like when a string is sliced without a step, we just call the native slice method. This by default returns a substring of that string, and not an Array.

Later on the instance check tries to join the string, which is an invalid method.