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System events are cool
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In JavaScript programming, you can use
code block functions to handle events.
0:00
There are two types of
events that can occur.
0:05
A user event or a system event.
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An example of a user
event is a mouse click.
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When a mouse click happens on the button,
the callback is triggered and
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then an alert is shown.
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An example of a system event
is the setTimeout function.
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A call back gets executed
after a given time.
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The developer may define the time
when the call back gets executed, but
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the system is what triggers it.
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Another example of a system event is
the ready state change of an Ajax request.
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[SOUND] The ready state change handler
gets triggered by the system when
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it goes through different
stages of the request.
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For example, when it sends the request,
when it loads data in, and
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when it's finished.
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Node.js has a number of system events
like reading data from a URL or
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file, when an action is completed,
and various error handling events.
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We'll cover these throughout this course.
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