functions working - first checkpoint

main.js

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+// 1. `.length`
+//    * Create an array called `cars` which consists of 4 different types of cars as String type. The first car type should be Ford.
+//    * Console.log the length of the array.
+//    * Use `node main.js` to run the program.
+
+const cars = ["ford", "chevy", "honda", "buick"];
+console.log(cars.length);
+
+// 1. `.concat()`
+//    * Create another array called `moreCars` with 4 more different types of cars. The last car type should be Honda.
+//    * Use the `concat` method to combine the `cars` and `moreCars` arrays into another array called `totalCars`.
+//    * Console.log the new array.
+//    * Run the program.
+
+const moreCars = ["hyndai", "tesla", "BMW", "GMC"];
+const totalCars = cars.concat(moreCars);
+console.log(totalCars);
+
+// 1. `.indexOf()` and `.lastIndexOf()`
+//    * Use the `indexOf` method to console.log the index of `Honda` in `totalCars`.
+//    * Use the `lastIndexOf` method to console.log the index of `Ford` in `totalCars`.
+//    * Run the program.
+console.log(totalCars.indexOf("honda"));
+console.log(totalCars.lastIndexOf("ford"));
+// 1. `.join()`
+//    * Use the `join` method to convert the array `totalCars` into a string called `stringOfCars`.
+//    * Console.log `stringOfCars`.
+//    * Run the program.
+const stringOfCars = totalCars.join(" ");
+console.log(stringOfCars);
+// 1. `.split()`
+//    * Use the `split` method to convert `stringOfCars` into an array called `carsFromString`.
+//    * Console.log the array you just created.
+//    * Run the program.
+//     > BONUS: Go back and pass a comma (`','`) in as an argument to `.split()` to separate the cars into individual items in the array. This is called a *separator* and it can be any character you wish to separate strings by.
+const carsFromString = stringOfCars.split(" ");
+console.log(carsFromString);
+// 1. `.reverse()`
+//    * Use the `reverse` method to create an array `carsInReverse` which is the array `totalCars` in reverse.
+//    * Console.log `carsInReverse`.
+//    * Run the program.
+const carsInReverse = totalCars.reverse();
+console.log(carsInReverse);
+// 1. `.sort()`
+//    * Use the `sort` method to put the array `carsInReverse` into alphabetical order.
+//    * Based on the types of cars you used, predict which item in the array should be at index 0.
+//    * Use the following code to confirm or reject your prediction: `console.log(carsInReverse.indexOf('yourPrediction'));`
+
+carsInReverse.sort();
+// BMW would be the first item in alphabetical order
+console.log(carsInReverse.indexOf("BMW"));
+
+// 1. `.slice()`
+//    * Create a `pets` array by copy/pasting the following: `const pets = ['dog', 'cat', 'fish', 'rabbit', 'snake', 'lizard', 'bird']`
+//    * Use the `slice` method to create a `reptiles` array with `snake` and `lizard` from the `pets` array.
+//    * Console.log the `reptiles` array and run the program.
+//    * Now console.log the `pets` array and run the program. Why do you think `snake` and `lizard` are still in the original array?
+
+const pets = ["dog", "cat", "fish", "rabbit", "snake", "lizard", "bird"];
+const reptiles = pets.slice(4, 6);
+console.log(reptiles);
+// the slice method does not modify the original array reference.
+console.log(pets);
+
+// 1. `.splice()`
+//    * Create a new array called `removedReptiles`, using the `splice` method to remove `snake` and `lizard` from the `pets` array.
+//    * Console.log `removedReptiles` and `pets` and run the program.
+//    * Go back and add the string `'hamster'` in as a third parameter to your `splice` method, then run the program again and notice how the `pets` array has changed. Do you see how that works?
+
+const removedReptiles = pets.splice(4, 2, "hamster");
+console.log(`removed reptiles:`, removedReptiles);
+console.log(`pets:`, pets);
+// splice parameters: splice(start, deleteCount, item0, item1, /* … ,*/ itemN)
+
+// 1. `.pop()`
+//    * Use the `pop` method to remove the last item from the `pets` array, saving it to a variable called `removedPet`.
+//    * Console.log `removedPet` and `pets` and run the program.
+
+const removedPet = pets.pop();
+// removes LAST element from original array reference and returns it.
+console.log(`removedPet:`, removedPet);
+console.log(`pets:`, pets);
+
+// 1. `.push()`
+//    * Use the `push` method to add `removedPet` back to the end of the `pets` array.
+//    * Console.log `pets` and run the program.
+
+pets.push(removedPet);
+// adds element to the end of original array reference.
+console.log(`pets.push(removedPet) =`, pets);
+
+// 1. `.shift()`
+//    * Use the `shift` method to remove and console.log the first item in the `pets` array.
+
+console.log(`pets.shift() = `, pets.shift());
+// removes FIRST element from original array reference
+
+// 1. `.unshift()`
+//    * Use the `unshift` method to add the string `'turtle'` as the first item in the `pets` array.
+//    * Console.log the `pets` array and run the program. If all went according to plan, you should see `['turtle', 'cat', 'fish', 'rabbit', 'hamster', 'bird']`.
+
+pets.unshift("turtle");
+// adds element to BEGINNING of original array reference.
+console.log(`pets after unshift method:`, pets);
+
+// 1. `.forEach()`
+//    * Create a numbers array by copy/pasting the following: `const numbers = [23, 45, 0 , 2, 8, 44, 100, 1, 3, 91, 34]`
+//    * Write code that will add 2 to each item in the array `numbers`.
+//       * `forEach` requires a function to be passed into it as its first argument.
+//       * Build a function called `addTwo` that can take in num, index, and arr as parameters—`(num, index, arr)`—and returns `num + 2` at each `index` of the `arr`.
+//       * Use `.forEach()` on the `numbers` array, passing in your freshly built function `addTwo` as an argument, in order to add 2 to each number in the array.
+//    * Console.log `numbers` and run the program.
+const numbers = [23, 45, 0, 2, 8, 44, 100, 1, 3, 91, 34];
+function addTwo(num, index, arr) {
+  arr[index] = num + 2;
+}
+numbers.forEach(addTwo);
+console.log(numbers);