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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Adding Classes

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. So you don't have access to higher-up elements like the <html> tag. If you want to add classes there that can affect the whole document, this is the place to do it.

About the <head>

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. If you need things in the <head> of the document, put that code here.

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

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Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.

All packages are different, so refer to their docs for how they work.

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HTML 

              
                <div id="app">
  <!-- value属性バインディング-->
  <input type="text" v-bind:value="text_caption">
  
  <!-- [オブジェクト構文 例１] -->
  <div v-bind:class="{ font_large: large_flg }">
    文字サイズサンプル(大)
  </div>
  
  <!-- [オブジェクト構文 例２] -->
  <div class="static" v-bind:class="{ active: active_flg, text_warning: warning_flg}"
>
    注意色サンプル
  </div>
  
  <!-- [オブジェクト構文 例３] -->
  <div class="static" v-bind:class="dangerObject">
    警告文字サンプル
  </div>
  
  <!-- [配列構文 例1] -->
  <div>
    <span>テストメッセージ：</span>
    <span v-bind:class="[activeClass,dangerClass]">
      警告テスト
    </span>
  </div>
</div>
!

CSS 

              
                /*文字サイズ設定*/
.font_large{
  font-size:32px;
}

/*activeクラス指定時*/
.active{
  font-weight:bold;
}

/*文字色パターン設定*/
.text_warning{
  color:#FFC607; /*注意色*/
}
.text_danger{
  color:red;    /*警告色*/
}
!

JS 

              
                const app = Vue.createApp({
  data: () => ({
    
    // テキストへの文字列表示設定
    text_caption: '表示テスト',
    
    // 文字サイズサンプル(大)設定プロパティ
    large_flg: true,
    
    // 注意色サンプル 設定プロパティ
    active_flg: false,
    warning_flg: true,
    
    // 警告文字サンプル 設定プロパティ
    dangerObject: {
      active: true,
      text_danger: true
    },
    
    // 警告テスト 設定プロパティ
    activeClass: 'font_large',
    dangerClass: 'text_danger'
    
  })
})
app.mount('#app')
!
999px

Console