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Great question.
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0.96
Yeah.
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0.681
AUDIENCE: Um-- You cannot do 0.1 for example.
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3.768
[INAUDIBLE]
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3.301
JORDAN: So, if we did o.1, yeah, so, o.1, 1 here, since we're
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5.22
typing it here, is a number.
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2.16
And we cannot set keys to numbers.
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But if it were an object literal like this,
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2.16
[TYPING]
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2.16
JORDAN: It considers this not to be a number, but rather a string.
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4.71
AUDIENCE: You can the array assignment by putting brackets around the one
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4.95
and passing it as a string, so you can do 0 dot
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2.475
[TYPING]
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1.485
AUDIENCE: Our brackets around [INAUDIBLE] o
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dot open bracket, open braces, and then, quotes, one.
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6.683
And then set that to a value.
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4.005
JORDAN: So, I think you mean this?
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1.85
[TYPING]
1,972.91
5
Yep.
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0.5
And I believe you can also do this.
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1.458
[TYPING]
1,982.82
1.62
Because that will get cast to a number.
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2.15
I mean a string.
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2.79
Any other questions?
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3.415
Cool-- yeah?
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0.956
AUDIENCE: If you have want the number one inside the bracket notation,
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5.757
versus the string one inside the bracket notation,
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3.283
it will be treated as the same keys?
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1.879
JORDAN: Yeah, so the question is, what is the difference between this here,
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and this here?
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1.7
The difference is, anything between the brackets
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4.12
will get coerced into a string.
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1.99
And so, since this is already a string, it's just that string one.
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3.756
Since this is not of type string, it actually
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gets implicitly coerced into a string.
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3.04
And so, like we saw earlier, if we did one plus some empty string,
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we get back the string one.
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1.59
So this becomes a string one, and it will index into that.
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3.06
Whereas, this number here, so if we did o3.1,
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3.427
[TYPING]
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3.663
That one does not actually get coerced, like it does between the brackets here.
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6.3
So JavaScript is basically saying, hey, this doesn't really make sense.
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3.99
I need a string here, not a number.
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3.7
Cool, any other questions?
2,054.83
1.532
Great-- So, let's talk a little bit about this thing, where
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4.897
I was talking about mutating objects.
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5.127
So say--
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0.499
[TYPING]
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3.225
So, say I had this object, so--
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2.224
In it we had, a gets a, b gets b.
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5.28
So say I wanted to change a to be something else?
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How might I do that?
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1.02
Yes.
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0.51
AUDIENCE: dot a equals--
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1
JORDAN: Yes, so I can update this to be anything else.
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2.46
[TYPING]
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3.24
Cool, but say I actually did this.
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1.875
[TYPING]
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2.715
Anybody care to guess what would be console logged here?
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2.84
So basically, what he's doing is, we're creating a new object.
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And storing it in o.
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This object has two keys, a and b, where their values are a and b respectively.
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I'm creating this new object called o2, and assign a value of o.
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I then go reset o.
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2.46
Not o2 but o.a to be a new value.
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And I'm going to console log o2.a.
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2.88
Anybody care to guess what this is going to console log?
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2.59
Yeah.
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0.5
AUDIENCE: a?
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1.5
JORDAN: So, a guess is a.
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1.71
What would be the alternative guess?
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2.937
AUDIENCE: New value.
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0.833
JORDAN: New value--
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2.113
[INAUDIBLE]
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1.867
JORDAN: Yeah, so let's run that.
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2.27
So you get new value.
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0.93
And so I talked about this thing called passing by reference,
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2.541
and passing by value.
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2.659
So, basically what's happening here, is that o is being said,
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6.08
hey, give me a new object, somewhere.
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4.14
And then store inside of it, a and b.
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2.64
And then o2 says hey, give me another object and set it to o.
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4.11
And rather then creating a new object, with the same keys and values,
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it's actually pointing to that same object.
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2.279
So this is a case where things are getting stored
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by reference, rather than by value.
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2.15
Meaning, so in CS50, we talked a little bit about pointers,
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and this is the exact same concept.
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Where these objects are not stored as entire serialized objects,
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but rather as references to these objects in memory.
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3.53
So o and o2 are both referencing that same exact object.
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3.7
So when we go back and say, hey update o.a to be new value,
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4.71
it's changing this object here, and still
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2.06
o and o2 are both pointing to that same object.
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3.43
So if I were to have updated 02 here, and console logged o.a,
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we would get that same result. Because o and o2 are still both referring to that
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same object in memory, and we're still updating that object here.
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3.97
Does that make sense?
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2.65
Yeah.
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0.61
AUDIENCE: So what if you wanted them to be different.
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2.208