- Practice writing arrays
- Practice using destructive methods to manipulate arrays
- Practice using nondestructive methods to manipulate arrays
We've learned about how arrays work and about the array methods built in to JavaScript that we can use to manipulate them. Now it's time to practice what we've learned.
If you haven't already, fork and clone this lab into your local environment.
Navigate into its directory in the terminal, then run code . to open the files
in Visual Studio Code.
Open up the test folder and take a look at indexTest.js. Note that some of
the names of the functions you will be writing begin with destructively and
some don't. This is a clue as to which Array method you will need to use for
each function.
Note also that the first test asks for an array called cats, set to an
initial value of ["Milo", "Otis", "Garfield"]. In your functions, you will be
accessing and manipulating this array.
Near the top of indexTest.js you will see the following:
beforeEach(function () {
cats.length = 0;
cats.push("Milo", "Otis", "Garfield");
});What this code does is reset the array to its original contents before each
test is run. The reason we need to do this is because some of your functions
will be destructive — they will change the original cats array. This
is a problem because it means the input to the remaining functions will be
dependent on the outcome of other functions. It also means that the expected
return value of a function might change if the tests are run in a different
order. This makes it more difficult both to write tests in the first place and
to figure out how to get the tests to pass. Resetting the array returns us to a
blank slate between tests.
This is also a good illustration of why it's generally good practice to avoid mutating a program's state whenever possible. If we use only nondestructive methods, we have complete control over what's going into and coming out of the function. This makes our programs more robust, easier to maintain, and less prone to bugs.
Remember the workflow:
- Install the dependencies using
npm install. - Run the tests using
npm test. - Read the errors; vocalize what they're asking you to do.
- Write code; repeat steps 2 and 3 often until a test passes.
- Repeat as needed for the remaining tests.
After you have all the tests passing, remember to commit and push your changes up to GitHub, then submit your work to Canvas using CodeGrade.
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