You learned string methods: slice() for extracting, split() and join() for converting, replace() and replaceAll() for substituting, and trim() for cleaning.
You used the Math object for rounding, random numbers, and finding min/max. You parsed strings with parseInt() and parseFloat(), and formatted with toFixed() and padStart().
Remember: string methods return new strings. toFixed() returns a string. Math.random() returns to exclusive.