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24.9
Like, what if you wanted them to not point to the same thing?
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JORDAN: Yeah, so the question is, what if we
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wanted them to have the same value but be different references?
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How might we do that?
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There are two different ways.
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One, the more annoying way, would just be to type the whole thing out again.
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[TYPING]
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So now we're guaranteed that o and o2 are
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going to be different references to an object that is basically the same.
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And another way would be --
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there are multiple different ways to do this.
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The most common way in pure JavaScript, would be to do this--
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[TYPING]
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Whereby, object assigned is basically saying, hey, pass in to me
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a bunch of arguments.
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And every single argument, I'm going to merge into the previous one,
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those lose keys and values.
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And so this is saying, give me a brand new object.
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So I'm using the object literal here to mean a new object.
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And then merge into it, of the keys and values of this object called o.
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And so this is basically saying, give me new object,
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and then set all of the keys and values of o to be in there.
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So this is the way of cloning an object.
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But say we actually did this
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[TYPING]
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So, what do we expect this to now print out?
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So, we mentioned that line nine, we're taking the keys and values of o,
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and merging those into a new object.
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And then that line 11 we're taking o2, getting the dot object,
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so accessing the value with the key called object.
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And then setting that object's key called key to new value.
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And then now console logging o to object dot key.
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Yeah.
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AUDIENCE: So, new value?
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JORDAN: Yes, so this, so the guess is new value,
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and that is absolutely correct.
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So this, so-- line nine here is doing what's called a shallow copy.
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Which is just grabbing the keys and values of some object,
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and just setting those blindly into some other object.
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As opposed to what would be called a deep copy.
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Where that would take the keys and values.
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And then if the values are objects, you'd
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also take those objects keys and values.
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Do that recursively, and basically get every single layer deep cloned.
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But since object assigned just takes the keys and values dumbly,
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if we have an object in there, update that object's key.
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o.obj and o2.obj are still referencing that same object in memory,
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so since we updated--
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we mutated that object, it would update in both o2 and o.
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Does that makes sense?
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Great, any questions about this?
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Yeah.
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AUDIENCE: How would you do a deep copy?
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JORDAN: So, how would you do deep copy?
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That's a great question.
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There are multiple different ways.
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So most people would say use a library.
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Meaning, rather than implementing this thing on your own,
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just take somebody else's implementation.
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But lets, let's actually do that.
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That's a good question.
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So, how would we do a deep copy?
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[TYPING]
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So, I know we haven't talked a ton about JavaScript yet,
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but lets actually tried to do this together.
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So, let's call a function, deep copy.
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And we're going to pass into it some object.
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And how would we implement this, if we're guaranteed
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that no objects have values of objects?
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Meaning we are guaranteed not to have objects within objects.
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How might we do this?
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AUDIENCE: Check for the type of the key.
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JORDAN: Yes, so we can check for the type of every key.
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But if we're guaranteed that no values are going to be objects,
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we can just do a shallow copy right?
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Yeah.
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AUDIENCE: So check every value?
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And if it's, the value is [INAUDIBLE] we have to recursively deep copy that.
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JORDAN: Yeah.
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So hold that thought.
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Let's actually implement this as if we know that there
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are no objects inside of objects.
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So if that were true, we could just return the shallow copy right?
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So object.assign
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[TYPING]
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So this would be a perfectly valid implementation,
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if we knew that there's no such thing as objects within objects.
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But since there are, we're going to have to do some magic here.
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So, can you repeat your recommendation again?
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AUDIENCE: So, check if the--
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any of the values is an object.
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Then you can't just take that value into a new object,
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just to reference the same object, we need to deep copy that object,
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instead of just taking [INAUDIBLE].
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JORDAN: So basically, so check every single value,
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and see if it's an object.
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If it is an object, then go ahead and deep copy that object.
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Otherwise, return that value.
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Cool.
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So let's do that.
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