Svelte 条件元素类报告为语法错误 [英] Svelte conditional element class reported as a syntax error

问题描述

我正在根据 if 块的 Svelte 指南制作一个 if 块.看起来很简单，但 Svelte 认为这是一个语法错误:

[!] (svelte plugin) ParseError: Unexpected character '#'公共\js\templates\works.html3:<div class="slides js_slides">4:{#each 作为工作，索引}5:<div class="js_slide {#if index === currentIndex }selected{/if} {#if index === 0 }first{/if}">^6:<img src="/images/work/screenshots/{works[index].slug }-0.{works[index].imageExtension}"/>7:</div>

为什么 {#if index === currentIndex } 不被认为是有效的?如何在 Svelte 中执行条件?

我不能为每种可能的结果创建单独的class=块，但这是大量的工作.

解决方案

Blocks ({#if..., {#each... etc) can'不能在属性内部使用——它们只能定义标记的结构.

相反，约定是使用三元表达式...

<div class="js_slide{索引 === 当前索引 ?'选择':''}{索引 === 0 ?'第一的' : ''}><img src="/images/work/screenshots/{works[index].slug }-0.{works[index].imageExtension }"/>

...或使用助手:

<div class="js_slide {getClass(work, index, currentIndex)}"><img src="/images/work/screenshots/{works[index].slug }-0.{works[index].imageExtension }"/>

有些人喜欢做data-selected={index === currentIndex} 和data=first={index === 0} 和样式基于 [data-selected=true] 选择器.

I am making an if block per the Svelte Guide for if blocks. It seems simple enough, but Svelte thinks it's a syntax error:

[!] (svelte plugin) ParseError: Unexpected character '#'
public\js\templates\works.html
3:     <div class="slides js_slides">
4:       {#each works as work, index}
5:         <div class="js_slide {#if index === currentIndex }selected{/if} {#if index === 0 }first{/if}">
                                ^
6:           <img src="/images/work/screenshots/{ works[index].slug }-0.{ works[index].imageExtension }"/>
7:         </div>

Why isn't {#if index === currentIndex } considered valid? How can I do a conditional in Svelte?

Not I could create seperate class= blocks for every possible outcome, but that's a massive amount of work.

解决方案

Blocks ({#if..., {#each... etc) can't be used inside attributes — they can only define the structure of your markup.

Instead, the convention is to use ternary expressions...

<div class="
  js_slide
  {index === currentIndex ? 'selected' : ''}
  {index === 0 ? 'first' : ''}
">
  <img src="/images/work/screenshots/{ works[index].slug }-0.{ works[index].imageExtension }"/>
</div>

...or to use a helper:

<!-- language: lang-html -->

<div class="js_slide {getClass(work, index, currentIndex)}">
  <img src="/images/work/screenshots/{ works[index].slug }-0.{ works[index].imageExtension }"/>
</div>

Some people prefer to do things like data-selected={index === currentIndex} and data=first={index === 0}, and style based on [data-selected=true] selectors instead.

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