Code use in PPR

I have a couple of students using builtin JavaScript methods such as array.splice() that were not discussed in class. The students are using these methods as part of program code they want to include on their PPR (a much longer and more robust procedure they came up with themselves).

They are still allowed to use their method (despite 1-2 lines of cited code due to these builtins) as part of their PPR, correct?

Yes - built in javascript codes are part of javascript! It is okay if they are not explicitly App Lab blocks.