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Get a crash course in using Vue's transition component to animate the flashcard flip.
Vue doesn't provide built-in
animation methods like jQuery, but
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it does make it easier for
you to use animation libraries, and
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offers a simple way to
coordinate transitions.
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That is, to create fun animations when
certain elements change, enter, or
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leave in an app.
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Vue saves you time by
coordinating the addition and
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removal of CSS classes for you.
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We can cross another item off of our list.
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For this video,
I'm going to assume that you have at least
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a little bit of knowledge of
the CSS transition property.
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If you don't, I'll leave some links to
some resources in the teacher's notes, but
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don't worry about it too much.
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The point of this video is not to teach
you about CSS transition effects, but
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rather, to make you aware of
the shortcuts that Vue can provide.
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Vue provides us with what's
known as a transition component.
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These components are beyond
the scope of this course,
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but they're essentially a way to
encapsulate small pieces of functionality
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in a way that is reusable and
maintainable.
0:57
So we'll start by surrounding
our card paragraph divs in
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the transition component.
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You'll notice that it looks
a lot like an HTML element.
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We also need to give the component a name,
I'll show you why in a moment.
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We'll name the transition component
something descriptive, like flip.
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For a visual representation
of what we need to do next,
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let's visit the Vue.js docs again.
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I'm going to go to vuejs.org.
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Then to Learn > Guide, and then,
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I will scroll down to
Enter/Leave & List Transitions.
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Then scroll down, and
have a look at this diagram.
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Vue provides six CSS classes that you can
use to write CSS for transition effects.
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Vue will then do all the heavy
lifting of determining when to add and
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remove these classes.
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So, if we think about our flipping card,
when the user clicks on it,
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the front of the card leaves,
and the back of the card enters.
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Or, on each click,
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one side of the card is disappearing as
the other side of the card is appearing.
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Right now,
that's happening instantaneously.
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The transition effects we write will
control how each card side looks
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as it's disappearing or reappearing.
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And that's when the enter and
leave classes are applied.
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We don't need to worry about enter-to and
leave-to for our animation, but
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these are classes that are applied one
frame after an element leaves or enters.
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And finally,
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the enter active and leave active classes
help us control the transition as a whole.
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All the options for
how long the transition should take,
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whether you want to ease the transition,
and so on.
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Let's go to styles.css.
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And you may need to scroll down a bit
to get to the classes that control
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the transition animation.
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Notice that all of the classes
start with the word flip.
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I could refer to these classes
simply as v-enter active or
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v-leave active and so on,
as we saw on the docs.
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But remember when we gave
the transition component the name flip?
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Because we've given this
transition component a name,
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Vue automatically knows that classes
called flip-enter or flip-leave,
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etc., are all classes that I'm going
to use with a component named flip.
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So if we were to use the transition
component again, for
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another animation in this template,
I could assign it a different name.
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And that would help Vue and me
differentiate between the two in my code.
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The enter active property is how I can
control the whole entering transition.
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So basically, I'm saying here,
when the front or
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back of the card enters,
I want the effect to last for 0.4 seconds.
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Flip enters how I specify it,
how I want the element to change.
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I want a card side to rotate
180 degrees as it enters.
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The opacity of 0 helps the transition
look a little smoother, and
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prevents you from seeing the card's
text backwards as it transitions in.
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You can remove that line and
have a look, if you're curious.
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Finally, when the front or
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back of the cart leaves, I want it to
just disappear, be removed from the dong.
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So I'm setting it to display none.
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So that's our CSS, but
this won't work quite yet.
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Because we're using the transition
component on more than one item,
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we're using it for two paragraphs, Vue
needs a way to tell these two items apart.
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To do that,
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we need to give a key to the elements
we're applying transition effects to.
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So, for this first paragraph,
I'll add a key attribute named "front".
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And for the second paragraph,
I'll add a key called "back".
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Let's check this out in the browser.
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So, I'm no animator, but I think we've
got a fairly good-looking flip animation,
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each time a card is clicked.
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If we open the Elements tab really quick,
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we can see that Vue is applying
these classes at the right time,
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without us having to write
any additional JavaScript.
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