Not an issue.

Same here.

Non, "If such an element is found, some immediately returns true. Otherwise, ..."

some returns -1

right?

some executes the callback function once for each element present in the array until it finds one where callback returns a true value. If such an element is found, some immediately returns true. Otherwise, some returns false.

The slope of a vertical line is not infinity, it does not exist.

The purpose of this kata is simply to figure out what number comes next in the sequence, and then return that number. It's just supposed to be fun, not to teach you anything.

Indeed. I try to fix it....Thank~

Are you mean something like this?

defaultArguments(add, {func: 1});