- Before you start
- Question 1: addToFrontOrBack() - SIDE EFFECTS
- Question 2: reverseString() - PURE
- Question 3: newArrayFullOf() - PURE
- Question 4: insertIntoMiddle() - SIDE EFFECT
- Question 5: deleteFromMiddle() - SIDE EFFECT
- Question 6: isRightIndex - PURE
- Question 7: roundAllNumsDown - PURE
- Question 8: getAllYCoordinates - PURE
- Question 9: MODIFY - uppercaseAll
- Question 10: MODIFY - destructureCoordinates
- Question 11: DEBUG - clearAll
- Question 12: DEBUG - getFirstItem
- Bonus: Really understand pass by value/reference
As you know, tonight's assignment is all about arrays! We covered a lot in class, but you'll have to read the docs for a few more array methods. Also, please see the ref-examples/ for some examples and graphics about "pass by value" and "pass by reference."
Also, remember that in "Functional Programming" a pure function is one that:
- always gives the same outputs given the same inputs
- has no side effects
A side effect is something like altering global state or mutating an argument. Now that we actually have a data type that can be mutated (arrays), we have to be on the watchout for this! Only mutate when you mean to, and make copies or new arrays for all others!
Write a function addToFrontOrBack() that takes 3 args: an array arr, a value of any type value, and a boolean isFront. Insert the value as either the first or last value in the arr, depending on the boolean isFront. The function should mutate the array and return nothing.
Write a function reverseString() that takes a string argument. The function should return a reversed version of the string. Will this function modify the original string in any way? Food for thought.
Before you go crazy with loops or anything, check out these three methods which can be combined to reverse a string:
Now, if you want to manually do this with loops, go crazy! It's fun, but know there's a common way to do this.
Write a function newArrayFullOf() that takes 2 args: a value of any type value and a number numOfValue. Your function should return a new array full of the value. Like this:
const arr = newArrayFullOf(1, 5)
// [1, 1, 1, 1, 1]
const arr2 = newArrayFullOf(true, 2)
// [true, true]This might be a stumper, but try experimenting with new Array() and perhaps some sort of a fill method? HmmmmMMMMmmm?.
This is a cool trick to know, I can't wait till you learn it too!
Write a function insertIntoMiddle() that takes 2 args: an array arr and a value of any type value. The function should find the middle index of the array and then insert the value there. The function is mutational so it returns nothing.
Check the tests to see exactly which index should be the "middle." Don't overthink it!
Write a function deleteFromMiddle() that takes an array arr. The function should delete whatever value is in the middle index of the array. The function is mutational so it returns nothing.
Check the tests to see exactly which index should be the "middle." Don't overthink it!
Write a function isRightIndex that takes 3 args: an array arr, a primitive type value, and a number index. The function returns a boolean, true if the given value is at the index in the arr, and false otherwise. That includes false for values that aren't even in the array.
Write a function roundAllNumsDown() that takes an array of numbers arr. This function should return a new array full of arrs numbers rounded down. The original arr numbers should not be modified in any way.
Write a function getAllYCoordinates() that takes an array of coordinate pairs arrOfCoords. This function should return a new array full of only the y coordinates (that is the second value in the coordinate arrays). Like this:
// [x, y]
getAllYCoordinates([[1, 2], [3, 4], [5, 6]])
// [2, 4, 6]
// [x, y, z]
getAllYCoordinates([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
// [2, 5, 8]This is technically a matrix function. How about that? You've barely started Marcy, and you're already parsing matrices? I'd be pretty proud of myself if I were you.
We have a function in modify.js that takes 3 words, upper cases them, and then returns them in an array. However...it's static. What if I pass in 2 words? Or 5? None? All it works with right now is 3 exactly. You should read the docs for the rest operator to improve this function.
Remember, we will never pass in an array as an argument, only individual word arguments.
We have a function in modify.js that takes a single coordinate array ([x,y]) and then returns a template string with them in it. It's not using modern destructuring syntax though and that's lame. Modify this function to use destructuring but keep the variable names x and y. Our tests are explicitly looking for those, and I want you to get the points.
In debug.js we have a broken function clearArr(). It's supposed to mutate a given array by deleting all the the values inside of it. But it's not working. Can you fix it and pass the tests?
In debug.js we have another broken function getFirstItem() that is not supposed to mutate the given array. We just want the first item of the array. Can you fix it?
We've been passing references and values throughout this assignment, but do you really understand the concept? We'll talk about it again throughout this module, but if you're done, check out the ref-examples/ directory. There's some graphics and example code in there. Play around with them!
A question to grapple with is this:
const arr1 = [1, 2, 3, 4]
const arr2 = [5, 6, 7, 8];
const bigArr1 = [arr1, arr2];
const bigArr2 = [...bigArr1];
arr1.push('oh dear');
console.log(bigArr1)
console.log(bigArr2)What does that log and why? We've talked about copying arrays, but called them "shallow" copies. Why?
"Pass by Reference" and "Pass by Value" are weird concepts for some, but once you get them (and you all will), a paradigm shift occurs in your brain. You'll start to see data types and functions differently. It's cool, we can't wait!