Learn JavaScript #14 | Arrays Part 3

Let me clear this out before we start on the next video. Alright, so, what we're going to do in this video is learn how to get the index number of an array, and then how we can use that. So, I'm going to type hobbies, I'm going to store this in a variable. So, I'm going to type indexNum, and it's going to be equal to our array. So hobbies, actually let me refresh entirely here so we have the full hobbies list. What we're going to do is we're going to do is get the index number of this, so counting from 0 this will be 0, 1, 2. So, this has an index number of 2 in the array, reading. So what we're going to do is we're going to create the variable indexNum, it's going to be equal to hobbies.indexOf, and we're going to be looking for 'reading.' So now if I type indexNum it's going to return the number 2 because that is the index number 2 inside of the array. So how we remove items from an array specifically, so if we wanted to remove item at index number 5 you know we could do that as well. For right now, we're going to remove index number 2. So we're going to remove reading from hobbies, and how we're going to do that is we are going to type hobbies.splice. And now this method takes two parameters. The first one is the position that we start at, and so if we typed 2 here it's going to start at reading. So this is going to be the first one that it removes, and then we can remove however many numbers at that point. So if I wanted to remove just one, we're just going to remove a reading from this list, the two variables that it takes in is 2 and 1. Now, let's pretend that I don't know that I'm removing index number 2. So I'm going to use our variable indexNum, and we're going to remove reading. Now if I type hobbies you'll see that that has been removed. Now, I'm going to remove gaming, programming, and music using the same methods. So hobbies.splice, I'm going to splice from position one, I'm going to remove three items. Now if I type hobbies we get blacksmithing and archery. This is now, these are now our hobbies. So, that's how to get started with arrays. Now there's one other practical use for index of, and that's to evaluate whether or not a certain item is in the array. So, let's go ahead and write an if statement, and I'm going to write this in here, and the if statement is going to be if hobbies.indexOf('reading') is greater than minus 1, that means reading is in the array. So I'm going to console.log "I like reading!" I'm going to remove that for each, and then we're going to test another. if(hobbies.indexOf let's say 'sports') is more than minus 1 that means sports is in the array, which it's not, so what we're going to do is else console.log("not in array") I'm going to save this and I'm going to refresh it, and we'll see I like reading and then not in array because this returns an indexed number that is 0 or greater. This can either be at index 0 or greater. If this is not found at all, the index of method is going to return the number minus 1. So, we could alternatively do this to test if something is not in the array, oops, we can say if it equals minus 1. I'm going to save it, I'm going to refresh, and it still says not in array. Now I used three equal signs here. This basically means not found, so we're checking if hobbies, sports, is not found. Now, we can do this with two, but that would return true if this was returned, right. So we're not comparing types, in that instance, we're comparing values, and certain values can be matched across types. For instance, true and true by using the two equal signs. So using three equal signs means does the value match and is it the same type, and so it's always safest to do this if you are looking for something specific in an application. If you're making any type of comparison that you know it needs to be one or the other, and it needs to be the same type, that's when you're going to use these. Alternatively, if it's not the same type you're going to use exclamation mark equals equals, and that's how we're going to work with that. So, I think we're all done with the arrays, next I would really like to move on to classes and building objects.