使用Svelte从API正确处理错误（Rails）

Question

我正在开发一个Svelte前端应用程序，该应用程序与Rails API服务器进行通信。我喜欢Rails的抽象方式（尤其是使用simple_form gem），并且希望为Svelte带来一些想法。我遇到的特定问题是如何将来自Rails服务器的错误与苗条的输入相关联]

首先，我从服务器调整了错误响应；通常，它们看起来像这样：

{ errors: 
  { generic: [<messages without association with particular field>], 
    email: ["Already taken", <msg_2>, ...], 
    password: ["Too short", ...],
    field_N: [...]
  }
}

generic错误可以是“无效的登录凭据”，“您的帐户被锁定”，“内部服务器错误”等。其他错误必须与表单字段相关，并且必须显示在它们旁边。

这是我目前的做法signup.svelte：

<script>
let email;
let password;
function registerRequest() {
  let regURL = baseURL+'/api/users/';
  let data = {"user": {"email": email, "password": password}};
  fetch(regURL, {
    method: 'POST',
    body: JSON.stringify(data),
    headers: {
      'Content-Type': 'application/json'
    }
  })
  .then(function(response) {
    if (!response.ok) {
      return response.json()
    } 
  })
  // if errors present then iterate through errors object
  .then(function(error) {
    // find id of the message field and insert actual messages
    for (let [key, value] of Object.entries(error.errors)) {
 document.getElementById(key).insertAdjacentHTML('beforeend',value);
    }
  });
}
</script>

<style> .errormessage { color: red; } </style>

<form class="col-sm-12 col-lg-6" on:submit|preventDefault={registerRequest}>
  <!-- here I need to create errormessage container for each field. -->
  <!-- first one is generic to display generic errors -->
  <div class="errormessage" id="generic"></div>

  <label for="UserEmail">Email address</label>
  <input type="email" class="form-control" id="UserEmail" aria-describedby="emailHelp" placeholder="Enter your email here..." bind:value={email}>
  <div class="errormessage" id="email"></div>

  <label for="UserPassword">Password</label>
  <input type="password" class="form-control" id="UserPassword" placeholder="...and your password here" bind:value={password}>
  <div class="errormessage" id="password"></div>

  <button type="submit" class="btn btn-primary">Register</button>
</form>

我想通过前端验证来统一上面的代码。如果显示errors对象-在带有错误的字段旁边显示消息。在我看来，使用getElementById是过大的。如果我的DOM从不重新加载，为什么要使用它？每次在input上它将搜索ID。也许应该是侦听器来侦听错误对象的更改？我试图将自定义event与Svelte绑定import { createEventDispatcher } from 'svelte';，但没有运气。

请帮助并分享您的想法。

Answer 1

您的直觉是正确的，在Svelte组件中使用getElementById会感到不舒服-通常Svelte希望您使代码成为代码[[declarative，其中DOM是状态的函数，而不是imperative您正在手动更改DOM。

对于错误消息，建议您在组件中使用errors变量。当服务器错误再次出现时，您可以将它们分配给errors，这将导致响应更新并重新呈现组件。这样，标记就可以知道在错误存在时呈现错误，而无需显式更改DOM。像这样的东西：

<script>
let email;
let password;
// New `errors` variable.
let errors = {};

function registerRequest() {
  // Reset the errors when the user submits a new request.
  errors = {};  

  let regURL = baseURL+'/api/users/';
  let data = {"user": {"email": email, "password": password}};
  fetch(regURL, {
    method: 'POST',
    body: JSON.stringify(data),
    headers: {
      'Content-Type': 'application/json'
    }
  })
  .then(function(response) {
    if (!response.ok) {
      return response.json()
    } 
  })
  .then(function(error) {
    // Just save the errors 
    errors = e.errors;
  });
}
</script>

<style> .errormessage { color: red; } </style>

<form class="col-sm-12 col-lg-6" on:submit|preventDefault={registerRequest}>
    <!-- first one is generic to display generic errors -->
    <!-- note the `|| []` part, which makes sure that
         `#each` won't throw an error when `errors.generic` doesn't exist -->
    {#each (errors.generic || []) as error}
    <div class="errormessage" id="generic">{error}</div>
    {/each}

  <label for="UserEmail">Email address</label>
  <input type="email" class="form-control" id="UserEmail" aria-describedby="emailHelp" placeholder="Enter your email here..." bind:value={email}>
    <!-- email errors -->
    {#each (errors.email || []) as error}
  <div class="errormessage" id="email">{error}</div>
    {/each}

  <label for="UserPassword">Password</label>
  <input type="password" class="form-control" id="UserPassword" placeholder="...and your password here" bind:value={password}>
    <!-- password errors -->
    {#each (errors.password || []) as error}
  <div class="errormessage" id="password">{error}</div>
    {/each}

  <button type="submit" class="btn btn-primary">Register</button>
</form>

这里是一个Svelte REPL，该代码正常工作。希望能有所帮助！