The data toolbox

You now know how to create values, work with them, and prepare for failure. This chapter turns to something else: three tools that always come up once you start talking to the outside world.

First, JSON. An object stays fine as long as it lives in memory, but to save it to a file or send it to another computer it has to become a plain string first. JSON.stringify converts a value into that string, and JSON.parse turns the string back into the original shape. This exchange becomes the foundation for the networking you will learn later in the course.

Second, Date. Questions like "what day is it today", "which of these two dates comes first", or "how many days are left" are awkward to answer with plain number arithmetic, because leap years and months of different lengths get in the way. You let a Date build the moment for you, then pull the year, month, and day back out of it, or compare two of them directly.

Third, regular expressions (RegExp). Questions like "does this look like a postal code" or "is this made only of digits" — checking whether a string follows a fixed shape — come up constantly. Instead of checking character by character with if, you write the pattern once and hand it to .test().

None of these three are "new syntax" the way earlier chapters were. This chapter is about getting comfortable with tools JavaScript already ships with — objects and their methods. That is exactly why there is so little to memorize, yet you will reach for them so often on the job.