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24.9
We'll talk about that a little more later.
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But for now, we'll just use this keyword called const.
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So if I want to declare a variable, I'd say const.
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So give me a variable called first name.
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And I can give it any value I want.
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So let's just call it my first name.
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So you notice I have a string literal there.
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It's using double quotes, and then I end that statement with a semi-colon.
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I can also do a last name.
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And if you notice, this time, I still have that string literal,
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but this time I'm using single quotes.
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Because in JavaScript there's really no difference
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between double and single quotes.
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You also notice I omitted that semi-colon, which in JavaScript is OK.
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So my colons are actually optional.
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So say I wanted something that was not a string.
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I can just give it a value, like 42.
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So in C, you might see something like, give me an int,
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or give me a string or a char star.
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You're declaring types right away with C,
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but for something like JavaScript, you actually don't have to do that.
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We can also do arrays.
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And we can just declare them in line like this, and I can have--
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So, if you notice, I actually have three different types all in this array.
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So I have a string, I have a number, and I have a function.
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And this is perfectly fine.
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JavaScript doesn't really care what you throw in an array.
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You can have all sorts of different variable types.
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And so say we want to access those things in an array.
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Anybody care to guess exactly how I would do that?
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So say I want to execute that function.
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How might I go about doing that?
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Any guesses?
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Yeah.
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Yeah, exactly.
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The array of two.
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So if you're familiar with other languages, a lot of them
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have the same syntax for indexing into an array.
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And so since we have three things in this array,
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we do what's called zero indexing, whereby the first index in that array
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is called the zeroth index.
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And then you count from there.
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So we have zeroth here, first, and second here.
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And so say I want to access that function.
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I just do array 2, and I get that function.
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And say I now wanted to execute that function.
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I can, say, execute it like that.
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So this is something that you might see in other languages,
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but JavaScript you can do it as well.
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You can just grab that function out of that array and execute it like that.
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Say I wanted a for loop, and I wanted to console log everything in that array.
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I can do it just almost like C. So I can do for--
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this time we'll use let for the variable.
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We'll talk a little more about that later.
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So I start at zero.
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Well i is less than the raised length.
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[TYPING]
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You might see me--
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my personal preference is to omit the semicolons,
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but you might read something online that has them.
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It really doesn't matter all that much.
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And so this line of code here.
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You might have seen a for loop in other languages that you've used.
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So this one is just saying for give me a variable that's
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called i that starts at zero.
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And while it's less than the number of values in the array--
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array.length-- just keep incrementing it.
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And then every single time console.log, which
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is JavaScript's print function, whatever that value in that array is.
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So we can actually run this.
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And as you see the first time, line 12, where
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we say index into that array to the second value, and call it.
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That's what's printing high.
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And this for loop here will now print string 42 and this thing called
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function, which is this function.
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Cool, any questions on syntax?
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Yeah.
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AUDIENCE: In your array there, does it matter if you
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have that third comma after your--
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JORDAN HAYASHI: It does not matter.
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So the question was, does it matter on line 9 that comment at the very end?
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And so JavaScript allows you to have trailing commas, meaning in arrays,
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objects, or even function calls.
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You can actually have extra commas, and it doesn't matter whether you have it
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or not.
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It's optional just like the semicolon is.
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But were I to omit the comma here and try
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to run that, I'm going to get a syntax error as expected.
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Cool, any other questions?
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Great.
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So back to slides.
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So types.
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So we talked about types a little bit earlier,
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and I'm just going to talk a little bit more about them.
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So JavaScript has what's called dynamic typing, meaning given a variable,
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it has no type associated with it.
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So just like I said, give me a variable called first name
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and set it equal to a string.
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I could actually change that later to, say, a type
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number or a Boolean or anything like that.
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