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And people often ask, hey, we're on ES6 now.
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There have been six different versions of JavaScript.
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Why don't you just change this to be null?
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And the answer that ECMA gives is, well, the whole internet would break.
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And so each new version of ECMAScript should definitely
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be backwards compatible with the previous versions.
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Otherwise, say I put out a website tomorrow.
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If somebody comes down and changes the JavaScript spec,
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then my website might break.
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And so a lot of websites actually rely on this to be true.
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And, therefore, if a breaking version of ECMAScript is released,
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it might actually just have unforeseen consequences.
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So this is just one of those strange JavaScript gotchas.
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Cool, so another good question would be so when should I use double equals
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versus triple equals?
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And people generally say you should never use double equals,
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because that means you have to know exactly how every single thing coerces.
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And not only you, but every single person who reads your code
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should know what all these values coerce do.
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And some of them might be somewhat surprising.
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So we have a chart here that talks about the JavaScript equality table.
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For those of you who have the slides opened, you can click on that link,
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and it will bring you to the repo that has this.
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Basically, some of these strings are somewhat strange.
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Like how empty array is double equals to false, which doesn't really
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make a ton of sense.
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A lot of these don't really make a ton of sense
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and, basically, never use that double equals because it
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might have some strange behaviors.
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So moving on with coercion.
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So we talked about coercing things into other types,
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but how about if we're getting to bools?
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So JavaScript has these things called falsy values.
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Who can name a falsy value?
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So falsy value is any value that, if cast to bool, becomes false.
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AUDIENCE: Two.
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JORDAN HAYASHI: Two?
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So two is actually truthy.
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So every number except for one number is truthy, well two numbers actually.
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AUDIENCE: Zero.
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JORDAN HAYASHI: Zero would be one of them, yeah.
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Not a number which is actually a number, of type number, is also a falsy value.
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Who can name another falsy value?
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AUDIENCE: Blank?
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JORDAN HAYASHI: Blank what?
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AUDIENCE: Or empty.
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JORDAN HAYASHI: Empty what?
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AUDIENCE: Empty array.
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JORDAN HAYASHI: Empty array is actually truthy.
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False is another one.
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Undefined, null.
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So those are the five falsy values.
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So who can name some truthy values?
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Somebody said two, which is a valid one.
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Three, four, every other number other than zero, negative zero, not a number.
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Empty array is also another truthy.
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Empty object and literally everything else.
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So anything other than those values right there are truthy.
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Cool, so objects, arrays, functions, objects.
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It looks like I put objects twice there, but I actually put it four times.
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So JavaScript has this weird thing where if it's not
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one of those primitive values, it's an object.
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And so we'll talk about this thing in a little bit
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called prototype inheritance, which talks
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about how these objects inherit from each other
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and how they actually work under the hood.
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But first let's compare those two types.
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So we talked about primitives earlier, which is--
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who can name some of the primitives?
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AUDIENCE: Null.
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JORDAN HAYASHI: Null, undefined.
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AUDIENCE: Number.
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JORDAN HAYASHI: Number.
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AUDIENCE: Boolean.
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JORDAN HAYASHI: Boolean.
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AUDIENCE: String.
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JORDAN HAYASHI: String.
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And simple.
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So good, you got them all.
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Nice.
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So everything other than those primitive types are actually objects.
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So primitives are immutable, which means if you
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want to change them, you're actually replacing them with a new value
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rather than actually changing them themselves, whereas objects are not.
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They're actually mutable.
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So who knows what storing by reference means?
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So storing by reference means we actually
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store a reference to this object thing, and we can actually
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change what is held there without actually changing
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where that thing is located in memory.
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We'll talk a little bit more about that in a second.
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But the opposite of that would be storing something
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by a value, which is what happens when you have primitives.
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So, like I said earlier, primitives are immutable,
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which means once you create a primitive, it can't actually be changed.
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And when you want to change something, you actually create a new primitive
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and replace the old one, whereas mutable things are actually
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stored by reference, and you can actually change that object.
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And so let's play with that a little bit.
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So there are a few different ways to create an object.
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