表单验证

HTML5 表单验证，通过浏览器默认行为或自定义样式和 JavaScript，为您的用户提供有价值的、可操作的反馈。

内容提要

我们知道目前客户端自定义验证样式和工具提示无法实现可访问性，因为它们没有暴露给辅助技术。在寻找解决方案时，我们建议使用服务器端选项或默认浏览器验证方法。

工作原理

下面是表单验证如何与 Bootstrap 一起工作：

HTML 表单验证通过 CSS 的两个伪类 :invalid 和 :valid 应用。它适用于 <input>、<select> 和 <textarea> 元素。
Bootstrap 将 :invalid 和 :valid 样式限定为父 .was-validated 类，通常应用于 <form>。否则，任何没有值的必填字段在页面加载时显示为无效。这样，您可以选择何时激活它们（通常在尝试提交表单之后）。
要重置表单的外观（例如，在使用 AJAX 提交动态表单的情况下），请从 <form> 中删除 .was-validated 类。
作为后备，可以使用 .is-invalid 和 .is-valid 类代替服务端验证的伪类。它们不需要 .was-validated 父类。
由于 CSS 工作方式的限制，我们不能（目前）在没有自定义 JavaScript 帮助的情况下将样式应用于 DOM 中表单控件之前的 <label>。
所有现代浏览器都支持约束验证 API，一系列用于验证表单控件的 JavaScript 方法。
反馈消息可能会使用浏览器默认值（每个浏览器不同，并且无法通过 CSS 设置样式）或带有额外 HTML 和 CSS 的自定义反馈样式。
您可以在 JavaScript 中使用 setCustomValidity 提供自定义有效性消息。

了解了这些，请考虑我们的自定义表单验证样式、可选的服务器端类和浏览器默认设置：

自定义样式

为了自定义 Bootstrap 表单验证消息，您需要将 novalidate 布尔属性添加到您的 <form>。这将禁用浏览器默认反馈工具提示，但仍提供表单验证 API 的 JavaScript 访问。尝试提交以下表格；我们的 JavaScript 将拦截提交按钮并将反馈转发给您。尝试提交时，您会看到应用于表单控件的 :invalid 和 :valid 样式。

自定义反馈样式应用自定义颜色、边框、焦点样式和背景图标以更好地传达反馈信息。 <select> 的背景图标仅适用于 .form-select，不适用于 .form-control。

<form class="row g-3 needs-validation" novalidate>
  <div class="col-md-4">
    <label for="validationCustom01" class="form-label">First name</label>
    <input type="text" class="form-control" id="validationCustom01" value="Mark" required>
    <div class="valid-feedback">
      Looks good!
    </div>
  </div>
  <div class="col-md-4">
    <label for="validationCustom02" class="form-label">Last name</label>
    <input type="text" class="form-control" id="validationCustom02" value="Otto" required>
    <div class="valid-feedback">
      Looks good!
    </div>
  </div>
  <div class="col-md-4">
    <label for="validationCustomUsername" class="form-label">Username</label>
    <div class="input-group has-validation">
      <span class="input-group-text" id="inputGroupPrepend">@</span>
      <input type="text" class="form-control" id="validationCustomUsername" aria-describedby="inputGroupPrepend" required>
      <div class="invalid-feedback">
        Please choose a username.
      </div>
    </div>
  </div>
  <div class="col-md-6">
    <label for="validationCustom03" class="form-label">City</label>
    <input type="text" class="form-control" id="validationCustom03" required>
    <div class="invalid-feedback">
      Please provide a valid city.
    </div>
  </div>
  <div class="col-md-3">
    <label for="validationCustom04" class="form-label">State</label>
    <select class="form-select" id="validationCustom04" required>
      <option selected disabled value="">Choose...</option>
      <option>...</option>
    </select>
    <div class="invalid-feedback">
      Please select a valid state.
    </div>
  </div>
  <div class="col-md-3">
    <label for="validationCustom05" class="form-label">Zip</label>
    <input type="text" class="form-control" id="validationCustom05" required>
    <div class="invalid-feedback">
      Please provide a valid zip.
    </div>
  </div>
  <div class="col-12">
    <div class="form-check">
      <input class="form-check-input" type="checkbox" value="" id="invalidCheck" required>
      <label class="form-check-label" for="invalidCheck">
        Agree to terms and conditions
      </label>
      <div class="invalid-feedback">
        You must agree before submitting.
      </div>
    </div>
  </div>
  <div class="col-12">
    <button class="btn btn-primary" type="submit">Submit form</button>
  </div>
</form>

// Example starter JavaScript for disabling form submissions if there are invalid fields
(function () {
  'use strict'

  // Fetch all the forms we want to apply custom Bootstrap validation styles to
  var forms = document.querySelectorAll('.needs-validation')

  // Loop over them and prevent submission
  Array.prototype.slice.call(forms)
    .forEach(function (form) {
      form.addEventListener('submit', function (event) {
        if (!form.checkValidity()) {
          event.preventDefault()
          event.stopPropagation()
        }

        form.classList.add('was-validated')
      }, false)
    })
})()

浏览器默认设置

对自定义验证反馈消息或编写 JavaScript 来更改表单行为不感兴趣？也可以正常工作，您可以使用浏览器默认设置。尝试提交下面的表格。根据您的浏览器和操作系统，您会看到略有不同的反馈风格。

虽然这些反馈样式无法使用 CSS 设置样式，但您仍然可以通过 JavaScript 自定义反馈文本。

<form class="row g-3">
  <div class="col-md-4">
    <label for="validationDefault01" class="form-label">First name</label>
    <input type="text" class="form-control" id="validationDefault01" value="Mark" required>
  </div>
  <div class="col-md-4">
    <label for="validationDefault02" class="form-label">Last name</label>
    <input type="text" class="form-control" id="validationDefault02" value="Otto" required>
  </div>
  <div class="col-md-4">
    <label for="validationDefaultUsername" class="form-label">Username</label>
    <div class="input-group">
      <span class="input-group-text" id="inputGroupPrepend2">@</span>
      <input type="text" class="form-control" id="validationDefaultUsername"  aria-describedby="inputGroupPrepend2" required>
    </div>
  </div>
  <div class="col-md-6">
    <label for="validationDefault03" class="form-label">City</label>
    <input type="text" class="form-control" id="validationDefault03" required>
  </div>
  <div class="col-md-3">
    <label for="validationDefault04" class="form-label">State</label>
    <select class="form-select" id="validationDefault04" required>
      <option selected disabled value="">Choose...</option>
      <option>...</option>
    </select>
  </div>
  <div class="col-md-3">
    <label for="validationDefault05" class="form-label">Zip</label>
    <input type="text" class="form-control" id="validationDefault05" required>
  </div>
  <div class="col-12">
    <div class="form-check">
      <input class="form-check-input" type="checkbox" value="" id="invalidCheck2" required>
      <label class="form-check-label" for="invalidCheck2">
        Agree to terms and conditions
      </label>
    </div>
  </div>
  <div class="col-12">
    <button class="btn btn-primary" type="submit">Submit form</button>
  </div>
</form>

服务端

我们建议使用客户端验证，但如果您需要服务器端验证，您可以使用 .is-invalid 和 .is-valid 指示无效和有效的表单字段。请注意，这些类也支持 .invalid-feedback。

对于无效字段，请确保使用 aria- describeby 将无效反馈/错误消息与相关表单字段相关联（注意此属性允许引用多个 id ，该字段已指向其他表单文本）。

要修复边界半径问题，输入组合框需要一个额外的.has-validation类。

<form class="row g-3">
  <div class="col-md-4">
    <label for="validationServer01" class="form-label">First name</label>
    <input type="text" class="form-control is-valid" id="validationServer01" value="Mark" required>
    <div class="valid-feedback">
      Looks good!
    </div>
  </div>
  <div class="col-md-4">
    <label for="validationServer02" class="form-label">Last name</label>
    <input type="text" class="form-control is-valid" id="validationServer02" value="Otto" required>
    <div class="valid-feedback">
      Looks good!
    </div>
  </div>
  <div class="col-md-4">
    <label for="validationServerUsername" class="form-label">Username</label>
    <div class="input-group has-validation">
      <span class="input-group-text" id="inputGroupPrepend3">@</span>
      <input type="text" class="form-control is-invalid" id="validationServerUsername" aria-describedby="inputGroupPrepend3 validationServerUsernameFeedback" required>
      <div id="validationServerUsernameFeedback" class="invalid-feedback">
        Please choose a username.
      </div>
    </div>
  </div>
  <div class="col-md-6">
    <label for="validationServer03" class="form-label">City</label>
    <input type="text" class="form-control is-invalid" id="validationServer03" aria-describedby="validationServer03Feedback" required>
    <div id="validationServer03Feedback" class="invalid-feedback">
      Please provide a valid city.
    </div>
  </div>
  <div class="col-md-3">
    <label for="validationServer04" class="form-label">State</label>
    <select class="form-select is-invalid" id="validationServer04" aria-describedby="validationServer04Feedback" required>
      <option selected disabled value="">Choose...</option>
      <option>...</option>
    </select>
    <div id="validationServer04Feedback" class="invalid-feedback">
      Please select a valid state.
    </div>
  </div>
  <div class="col-md-3">
    <label for="validationServer05" class="form-label">Zip</label>
    <input type="text" class="form-control is-invalid" id="validationServer05" aria-describedby="validationServer05Feedback" required>
    <div id="validationServer05Feedback" class="invalid-feedback">
      Please provide a valid zip.
    </div>
  </div>
  <div class="col-12">
    <div class="form-check">
      <input class="form-check-input is-invalid" type="checkbox" value="" id="invalidCheck3" aria-describedby="invalidCheck3Feedback" required>
      <label class="form-check-label" for="invalidCheck3">
        Agree to terms and conditions
      </label>
      <div id="invalidCheck3Feedback" class="invalid-feedback">
        You must agree before submitting.
      </div>
    </div>
  </div>
  <div class="col-12">
    <button class="btn btn-primary" type="submit">Submit form</button>
  </div>
</form>

支持的元素

验证样式可用于以下表单控件和组件：

<input>s 和 <textarea>s 添加了 .form-control 类（包括最多一个 .form-control 在输入组合框中）
<select>s 添加了 .form-select 类
.form-checks

<form class="was-validated">
  <div class="mb-3">
    <label for="validationTextarea" class="form-label">Textarea</label>
    <textarea class="form-control is-invalid" id="validationTextarea" placeholder="Required example textarea" required></textarea>
    <div class="invalid-feedback">
      Please enter a message in the textarea.
    </div>
  </div>

  <div class="form-check mb-3">
    <input type="checkbox" class="form-check-input" id="validationFormCheck1" required>
    <label class="form-check-label" for="validationFormCheck1">Check this checkbox</label>
    <div class="invalid-feedback">Example invalid feedback text</div>
  </div>

  <div class="form-check">
    <input type="radio" class="form-check-input" id="validationFormCheck2" name="radio-stacked" required>
    <label class="form-check-label" for="validationFormCheck2">Toggle this radio</label>
  </div>
  <div class="form-check mb-3">
    <input type="radio" class="form-check-input" id="validationFormCheck3" name="radio-stacked" required>
    <label class="form-check-label" for="validationFormCheck3">Or toggle this other radio</label>
    <div class="invalid-feedback">More example invalid feedback text</div>
  </div>

  <div class="mb-3">
    <select class="form-select" required aria-label="select example">
      <option value="">Open this select menu</option>
      <option value="1">One</option>
      <option value="2">Two</option>
      <option value="3">Three</option>
    </select>
    <div class="invalid-feedback">Example invalid select feedback</div>
  </div>

  <div class="mb-3">
    <input type="file" class="form-control" aria-label="file example" required>
    <div class="invalid-feedback">Example invalid form file feedback</div>
  </div>

  <div class="mb-3">
    <button class="btn btn-primary" type="submit" disabled>Submit form</button>
  </div>
</form>

提示工具

如果您的表单布局允许，您可以将 .{valid|invalid}-feedback 类替换为 .{valid|invalid}-tooltip 类以显示添加了样式的工具提示。确保有一个设置了 position: relative 的父级元素用于工具提示定位。在下面的示例中，我们的列类已经具有此设置，但您的项目可能还需要设置。

<form class="row g-3 needs-validation" novalidate>
  <div class="col-md-4 position-relative">
    <label for="validationTooltip01" class="form-label">First name</label>
    <input type="text" class="form-control" id="validationTooltip01" value="Mark" required>
    <div class="valid-tooltip">
      Looks good!
    </div>
  </div>
  <div class="col-md-4 position-relative">
    <label for="validationTooltip02" class="form-label">Last name</label>
    <input type="text" class="form-control" id="validationTooltip02" value="Otto" required>
    <div class="valid-tooltip">
      Looks good!
    </div>
  </div>
  <div class="col-md-4 position-relative">
    <label for="validationTooltipUsername" class="form-label">Username</label>
    <div class="input-group has-validation">
      <span class="input-group-text" id="validationTooltipUsernamePrepend">@</span>
      <input type="text" class="form-control" id="validationTooltipUsername" aria-describedby="validationTooltipUsernamePrepend" required>
      <div class="invalid-tooltip">
        Please choose a unique and valid username.
      </div>
    </div>
  </div>
  <div class="col-md-6 position-relative">
    <label for="validationTooltip03" class="form-label">City</label>
    <input type="text" class="form-control" id="validationTooltip03" required>
    <div class="invalid-tooltip">
      Please provide a valid city.
    </div>
  </div>
  <div class="col-md-3 position-relative">
    <label for="validationTooltip04" class="form-label">State</label>
    <select class="form-select" id="validationTooltip04" required>
      <option selected disabled value="">Choose...</option>
      <option>...</option>
    </select>
    <div class="invalid-tooltip">
      Please select a valid state.
    </div>
  </div>
  <div class="col-md-3 position-relative">
    <label for="validationTooltip05" class="form-label">Zip</label>
    <input type="text" class="form-control" id="validationTooltip05" required>
    <div class="invalid-tooltip">
      Please provide a valid zip.
    </div>
  </div>
  <div class="col-12">
    <button class="btn btn-primary" type="submit">Submit form</button>
  </div>
</form>

Sass

变量

$form-feedback-margin-top:          $form-text-margin-top;
$form-feedback-font-size:           $form-text-font-size;
$form-feedback-font-style:          $form-text-font-style;
$form-feedback-valid-color:         $success;
$form-feedback-invalid-color:       $danger;

$form-feedback-icon-valid-color:    $form-feedback-valid-color;
$form-feedback-icon-valid:          url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 8 8'><path fill='#{$form-feedback-icon-valid-color}' d='M2.3 6.73L.6 4.53c-.4-1.04.46-1.4 1.1-.8l1.1 1.4 3.4-3.8c.6-.63 1.6-.27 1.2.7l-4 4.6c-.43.5-.8.4-1.1.1z'/></svg>");
$form-feedback-icon-invalid-color:  $form-feedback-invalid-color;
$form-feedback-icon-invalid:        url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 12 12' width='12' height='12' fill='none' stroke='#{$form-feedback-icon-invalid-color}'><circle cx='6' cy='6' r='4.5'/><path stroke-linejoin='round' d='M5.8 3.6h.4L6 6.5z'/><circle cx='6' cy='8.2' r='.6' fill='#{$form-feedback-icon-invalid-color}' stroke='none'/></svg>");

Mixins

通过我们的 loop 将两个 mixin 组合在一起，以生成我们的表单验证反馈样式。

@mixin form-validation-state-selector($state) {
  @if ($state == "valid" or $state == "invalid") {
    .was-validated #{if(&, "&", "")}:#{$state},
    #{if(&, "&", "")}.is-#{$state} {
      @content;
    }
  } @else {
    #{if(&, "&", "")}.is-#{$state} {
      @content;
    }
  }
}

@mixin form-validation-state(
  $state,
  $color,
  $icon,
  $tooltip-color: color-contrast($color),
  $tooltip-bg-color: rgba($color, $form-feedback-tooltip-opacity),
  $focus-box-shadow: 0 0 $input-btn-focus-blur $input-focus-width rgba($color, $input-btn-focus-color-opacity)
) {
  .#{$state}-feedback {
    display: none;
    width: 100%;
    margin-top: $form-feedback-margin-top;
    @include font-size($form-feedback-font-size);
    font-style: $form-feedback-font-style;
    color: $color;
  }

  .#{$state}-tooltip {
    position: absolute;
    top: 100%;
    z-index: 5;
    display: none;
    max-width: 100%; // Contain to parent when possible
    padding: $form-feedback-tooltip-padding-y $form-feedback-tooltip-padding-x;
    margin-top: .1rem;
    @include font-size($form-feedback-tooltip-font-size);
    line-height: $form-feedback-tooltip-line-height;
    color: $tooltip-color;
    background-color: $tooltip-bg-color;
    @include border-radius($form-feedback-tooltip-border-radius);
  }

  @include form-validation-state-selector($state) {
    ~ .#{$state}-feedback,
    ~ .#{$state}-tooltip {
      display: block;
    }
  }

  .form-control {
    @include form-validation-state-selector($state) {
      border-color: $color;

      @if $enable-validation-icons {
        padding-right: $input-height-inner;
        background-image: escape-svg($icon);
        background-repeat: no-repeat;
        background-position: right $input-height-inner-quarter center;
        background-size: $input-height-inner-half $input-height-inner-half;
      }

      &:focus {
        border-color: $color;
        box-shadow: $focus-box-shadow;
      }
    }
  }

  // stylelint-disable-next-line selector-no-qualifying-type
  textarea.form-control {
    @include form-validation-state-selector($state) {
      @if $enable-validation-icons {
        padding-right: $input-height-inner;
        background-position: top $input-height-inner-quarter right $input-height-inner-quarter;
      }
    }
  }

  .form-select {
    @include form-validation-state-selector($state) {
      border-color: $color;

      @if $enable-validation-icons {
        &:not([multiple]):not([size]),
        &:not([multiple])[size="1"] {
          padding-right: $form-select-feedback-icon-padding-end;
          background-image: escape-svg($form-select-indicator), escape-svg($icon);
          background-position: $form-select-bg-position, $form-select-feedback-icon-position;
          background-size: $form-select-bg-size, $form-select-feedback-icon-size;
        }
      }

      &:focus {
        border-color: $color;
        box-shadow: $focus-box-shadow;
      }
    }
  }

  .form-check-input {
    @include form-validation-state-selector($state) {
      border-color: $color;

      &:checked {
        background-color: $color;
      }

      &:focus {
        box-shadow: $focus-box-shadow;
      }

      ~ .form-check-label {
        color: $color;
      }
    }
  }
  .form-check-inline .form-check-input {
    ~ .#{$state}-feedback {
      margin-left: .5em;
    }
  }

  .input-group .form-control,
  .input-group .form-select {
    @include form-validation-state-selector($state) {
      @if $state == "valid" {
        z-index: 1;
      } @else if $state == "invalid" {
        z-index: 2;
      }
      &:focus {
        z-index: 3;
      }
    }
  }
}

映射(Map)

这是来自 _variables.scss 的验证 Sass 映射。覆盖或扩展它以生成不同或额外的状态。

$form-validation-states: (
  "valid": (
    "color": $form-feedback-valid-color,
    "icon": $form-feedback-icon-valid
  ),
  "invalid": (
    "color": $form-feedback-invalid-color,
    "icon": $form-feedback-icon-invalid
  )
);

$form-validation-states 的映射可以包含三个可选参数来覆盖工具提示和焦点样式。

Loop

用于迭代 $form-validation-states 映射值以生成我们的验证样式。对上述 Sass 映射的任何修改都将通过此循环反映在您编译的 CSS 中。

@each $state, $data in $form-validation-states {
  @include form-validation-state($state, $data...);
}

自定义

验证状态可以通过 Sass 使用 $form-validation-states 映射进行自定义。这个 Sass 映射位于我们的 _variables.scss 文件中，是我们生成默认 valid/invalid 验证状态的方式。包括一个嵌套映射，用于自定义每个状态的颜色、图标、工具提示颜色和焦点阴影。虽然浏览器不支持其他状态，但使用自定义样式的用户可以轻松添加更复杂的表单反馈。

请注意，我们不建议在不修改 form-validation-state mixin 的情况下自定义 $form-validation-states 值。