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array.slice(a, b) doesn’t work the way you’re thinking. It takes a ‘slice’ out of the array starting at index a and ending at but not including index b. In your example, bananas is at index 1, and brown rice is at index 3. groceryList.slice(1, 4) will return ['banana's, 'coffee beans', 'brown rice']. These are the elements at indexes 1, 2, 3. Might seem kinda quirky, but that’s how it works. Hope this helps!
Check out this link:
One certainly hopes you bookmarked that site. W3C pipes everything to them to disseminate for us. We can rely on this without the aid of outside sources mimicking as w3.org.
Good question. I don’t really know. It does allow for using slice() without a 2nd parameter:
myArray[1, 2, 3, 4, 5];
console.log(myArray.slice(3)); //3 is the starting index (inclusive)
Output:
[4, 5]
With only 1 parameter, slice() uses it as the starting index, and returns all elements from that point through the end of the array. If we only wanted the element at index 3:
myArray[1, 2, 3, 4, 5];
console.log(myArray.slice(3, 4)); //4 is now the 'up-to, but not including' index
Hey @timmskiller, I was stuck with the same issue. I had to use a shell on my computer in order to understand the slice function. I think the problem comes in when when the MDN Documentation says to use the index. Based on the previous lesson we know the index on an array starts with 0, not one. But based on that I used the index 0 and not 1. It seems that for this function we need to use the 1 index as an entry and the last index past the one we would like to display. This is the code that I made
console.log("Creating an array named groceryList");
Why do almost all the array methods on MDN Web Docs have ‘prototype’ in them? And why doesn’t, for example, array.prototype.slice() work while array.slice() does in the codecademy editor?
Array.prototype.method() tells us that array objects inherit their methods from Array.prototype, not Array directly. Read up on the prototype object tied to each constructor in JS. It’s a bit more detailed than one can describe here.
Methods are invoked on the the array object, not on Array.prototype.
Recall that indexOf()always works from left to right regardless whether negative or positive indices used. By setting the startfrom index to -1, you are starting on the last element, and since it is not a 2, the return is -1 (not found).
Supplemental
Above we have found a method for determining if the last element is a given value.
array.indexOf(9, -1) // <- 2
While not entirely practical, we could weave this into an algo that can count occurrences of a value in an array. More play possibilities if you have the time to go down that rabbit hole.
array.slice(-1) === 9 // <- true
Another index tool is the sister of indexOf() => lastIndexOf() which works the exact same way, and returns -1 for not found. It too can be fashioned to count occurrences, or at least locate the last occurrence of a given value.
" Call .indexOf() on groceryList to find the index of the element 'pasta' and save the returned value to a const variable named pastaIndex. Then log pastaIndex to the console"
The index/returned value is ‘4’ so I thought the answer would be:
Compare the given solution to the instructions. Which one follows the instructions to the letter, that one, or yours?
The instructions don’t ask us to literally set the variable, but to use a method on the array to determine the value, and assign the derived value. If we somehow shift the list around, your value will then be incorrect. The derived (dynamic) value will always be correct. That’s why we have such tools.
The above is a literal assignment that assumes we know the index; i. e., have intimate beforehand knowledge of the contents and order of the array.
In a dynamic program with data streaming in or built from user inputs our program has no such intuition. This requires us to implement an Array method (array.indexOf()) so that we can supply any argument and if the term exists in the array, get its index.
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