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and
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go ahead and run that count function
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every 1000 milliseconds otherwise known
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as every one second go ahead and run the
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count function so now when I open
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counter dot HTML it's zero but every
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5.741
second now it's going to change every
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second updating one by one by one I
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3.509
don't have to click the button of course
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2.91
I could and the event handler would
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still work but the interval is saying
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now every one second go ahead and run
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the count function and that has this
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3.241
particular result so if you've ever seen
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a webpage that like displays the current
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time in seconds and like a countdown
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timer or is displaying the current time
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3.75
with seconds it might be doing something
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like this just having some sort of
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interval that every second is going to
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count and increment in order to say
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update the number to the one greater one
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greater and one greater than that of
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course if I close the page and go back
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to it if I close these pages and then
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open counter dot HTML again I've gone
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back to zero like JavaScript is not
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saving any state about my page it's just
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every time we're running the page it's
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going to go back to counter j/s it's
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4.02
going to say all right we're defining a
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variable called counter we're setting
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that variable equal to zero so every
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3.299
time I load the page it's going to be
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set back to zero and that might not be
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great depending on the type of page
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3.301
you're trying to create that maybe you
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3.571
want to page that is somehow able to
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store information such that on
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subsequent visits were able to utilize
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the information that was already stored
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some way of remembering information for
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later use in later versions of
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JavaScript and more modern browsers now
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allow us to do something just like that
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called local storage and what local
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storage is is it's a way for us to be
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able to store information inside of the
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user's web browser that a page can ask
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to store particular values inside the
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web browser and later on on subsequent
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visits to that page we can go back and
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say let's extract those values that were
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previously stored inside of local
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storage local storage it's going to give
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us access to two key functions that
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we're going to use to manipulate this
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local storage
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the first is local storage getitem where
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we would like to get something out of
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local storage based on its key some name
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that we have given to that value and we
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also have access to local storage dot
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set item which goes ahead and adds a new
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value to local storage or replaces an
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existing value in local storage
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setting this key equal to a particular
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value so we can use local storage then
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to allow our webpages using javascript
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to be able to store information and
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4.02
retrieve information from the browser
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4.38
and let's now try to use that in order
4,966.34
6.09
to solve this problem of the counter
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6.05
that seems to always reset back to zero
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5.01
so now in counter jeaious instead of
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sending counter equal to zero the first
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thing I want to know is is there already
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a value for the counter in local storage
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so I can ask a question like if local
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storage dot get item counter meaning go
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to local storage try and get the counter
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and anything in this if expression will
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happen if there is something inside of
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4.41
local storage for counter but it turns
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out that if I want to do the inverse of
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that say not I can just use the
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3.72
exclamation point much like in C in
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JavaScript the exclamation point just
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means not so meaning if there is not
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something in local storage called
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counter well then let's go ahead and
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just set the value in local storage
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local storage dot set item counter and
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we'll set it equal to zero so what this
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is doing here is before anything else
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happens we are checking local storage to
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say is there already a value for counter
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and if there is not already a value for
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counter we need to make sure there is
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something there inside of local storage
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