Learn JavaScript #17 | Functions - Multiple Parameters

Alright guys, so in this video we are going to follow along with the functions section here, and I'm going to talk about multiple values and a quick, dirty way to have however many values you want. So, what we're going to do is first to pass multiple variables into a function, it's literally as simple as putting a comma and then defining the second piece of data, or the second parameter. So, in this case, get phrase length is going to take phrase and another. So what we're going to do is we're going to add both of these lengths together, so I'm going to create two variables. I'll use this for one, so p1 is going to be equal to that, and then var p2 is going to be equal to "This is a shorter sentence." And then when we call the get phrase length we're going to pass in both. So I'm going to save this, and now I'm going to refresh, and it still says 34 because we still only do this. So what we're going to do is phrase.length + another.length. So we're going to save that, now we're going to refresh and it's going to say 61. So this is the total length of both of these strings here, and that's how to do two parameters. Now what happens if I just pass one into that function? When we refresh it can't get the second one. So it's going to fail because we assume that that parameter is being passed in. Now if I remove this, save it and refresh, it works just fine, and that's because this second parameter, as long as we don't reference it within this function, we could do something like this. If typeof another doesn't equal "undefined" then we can do l += another.length; and then save this. Now we're going to pass in p2, after we put a comma in that method call here, and I'm going to save it and refresh, now we get 61. So typeof is a way to check the type of something. So, if I say typeof this, it's going to say "object" because that's how we create an object, which we're going to get to in the next video. If I say typeof this, it's going to say "object" as well, even though it's an array. If I say typeof that, it's going to say a "number." It's going to say the same thing for a float, and a string. So as you can see typeof...now if I say typeof vf without putting this in quotations or anything, it's assumed that this is a variable, as you can tell here, and we haven't defined that variable. So typeof a variable that hasn't been created is going to return as a string representation of "undefined." So, that's how we can check going into this method, if typeof and then another does not equal undefined as a string. So, again, when you're using comparisons this means not, and by using not, equals, equals it means it is not the value, and not the type. So this is a string that represents the word undefined. If we don't pass that in, save and refresh, it just prints out 34 and it skips over this because this type of returns undefined, so then this doesn't even run if it's undefined. So that's a bit more about I guess variable error checking, I guess. Rather, existence, checking the existence of something, specifically a variable, and making sure it's not undefined before using it. Which shouldn't really be necessary except in this case where I'm trying to call it with only one, with only one parameter. Now, in the next video we're going to get to objects, and I think this is the end of the functions, at least for now.