Please consider the line of code below: var args = Array.prototype.slice.call(arguments); isn’t args = Array.prototype.slice.call(arguments) like doing : args = arguments.slice(), if not, why and what is the difference please explain if possible thanks More on forum.freecodecamp.org

For future posts, if you have a question about a specific challenge as it relates to your written code for that challenge, just click the Ask for Help button located on the challenge. It will create a new topic with all code you have written and include a link to the challenge also. More on forum.freecodecamp.org

Ok, lets start with 'lastIndexOf'. Imagine this const array = ['a', 'a', 'b', 'b', 'c', 'c', 'c'] Now what they ask you to do is tell them where in that array the last 'b' is located. So you do array.lastIndexOf('b') Which will give you the number 3, since the first position is 0. Now you can work with that information. Lets say you want to clear all the old data. The new data is the fancy 'c' the client wants, everything else is to be ignored. Slice takes two arguments, start of what you want to extract and end, but end is optional, which means you can just use the start. So if you know that the 'c' starts after 'b', your start will be the position after 'b'. lastIndexOf tells you where 'b' is, so you can combine them like this: const newArray = array.slice(array.lastIndexOf('b') + 1) This will return only the three 'c's. If you had used slice(2, 4), it would start at the 3rd element, which is a 'b', include the 4th element, also a 'b' and end at the 5th element (index 4). So it would ignore the rest and the new array would be ['b', 'b', 'c']. I'm on the phone in the train, so this could be poorly formatted and maybe not well explained, please let me know if so, I'll try again. More on reddit.com

Complex data types (Object, Array, etc.) are passed by reference. When you assign one of these data types to a variable, you are assigning a reference to it. // Pass by Reference example const letters = ["a", "b", "c"]; const favoriteLetters = letters; favoriteLetters.push("d"); console.log(letters); // ["a", "b", "c", "d"] console.log(favoriteLetters); // ["a", "b", "c", "d"] When we assign the reference to the letters array to favoriteLetters they share the same array. The same thing happens with nested arrays. You can copy an array with original_array.slice() or with the spread operator [...original_array], but these are called shallow clones. If the items in the array are Objects or Arrays, those are still references, rather than copies. To get a copy of nested items in the array as well, you need a deep clone. The easiest deep clone strategy is the one you include in your edit. const copy = JSON.parse(JSON.stringify(original_array)); More on reddit.com