91 lines
2.4 KiB
Markdown
91 lines
2.4 KiB
Markdown
---
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title: Declarative Rendering
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---
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## Instalation
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Before we get started, there are a couple of ways to use Vue.js, namely via CDN and via
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installation. For a first experience, it's easier to use the CDN.
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For development, use this:
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```html
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<!-- development version, includes helpful console warnings -->
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<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
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```
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When jumping to production, this:
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```html
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<!-- production version, optimized for size and speed -->
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<script src="https://cdn.jsdelivr.net/npm/vue"></script>
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```
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As mentioned before, you can also install the `vue-cli`, but this is not
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recomended for beginners.
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## Declarative Rendering
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Vue.js is a great tool for creating dynamic pages, and a first way to get in
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touch with that is what's called Declarative Rendering.
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The use of term "declarative" intends to straighten this concept to
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declarative languages, such as SQL: you order something, it's not implied
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any implementation. Vue.js allows you to declare what data you want to be
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rendered, as simply as that:
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```html
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<div id="app">
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{{ message }}
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</div>
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```
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```javascript
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let app = new Vue({
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el: '#app',
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data: {
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message: 'Hello, world!'
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}
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});
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```
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With those snippets, you're telling Vue to dynamically render whatever is stored
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inside `message` variable. And the fun: whenever `message` is changed,
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Vue.js manages to reload that specific part of the DOM and you see the
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change.
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If you want to try this reactivity out, open the console and change the value
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of `app.message` to say, `"Hello from console"`. Did you notice the change in
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the page?
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The `{{ ... }}` is the syntax for that behavior: outputting the value
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of a variable or of an expression. For instance, this is also a valid use and
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will result in `hello`:
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```html
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<div id="app">
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{{ 1 < 2 ? "hello" : "goodbye" }}
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</div>
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```
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There're cases in which what we want is to set an attribute using our Vue app's
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variable. You might think that the same syntax applies, but Vue has something
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specific for that, what we call "binding".
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```html
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<div id="app">
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<a v-bind:href="dynamicLink">This link</a>
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</div>
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```
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```javascript
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let app = new Vue({
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el: '#app',
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data: {
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dynamicLink: 'medium.freecodecamp.org'
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}
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}
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```
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The syntax `v-bind` is what Vue.js calls a "directive". It's a way to set a new
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attribute to the tag that will be handled by Vue -- there are more
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directives, they all begin with `v-`.
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