Form group

The <b-form-group> component is the easiest way to add some structure to forms. Its purpose is to pair form controls with a legend or label, and to provide help text and invalid/valid feedback text, as well as visual (color) contextual state feedback.

<template>
  <b-form-group
      id="fieldset1"
      description="Let us know your name."
      label="Enter your name"
      label-for="input1"
      :invalid-feedback="invalidFeedback"
      :valid-feedback="validFeedback"
      :state="state"
  >
    <b-form-input id="input1" :state="state" v-model.trim="name"></b-form-input>
  </b-form-group>
</template>

<script>
export default {
  computed: {
    state () {
      return this.name.length >= 4 ? true : false
    },
    invalidFeedback () {
      if (this.name.length > 4) {
        return ''
      } else if (this.name.length > 0) {
        return 'Enter at least 4 characters'
      } else {
        return 'Please enter something'
      }
    },
    validFeedback () {
      return this.state === true ? 'Thank you' : ''
    }
  },
  data () {
    return {
      name: ''
    }
  }
}
</script>

<!-- form-group-1.vue -->

Label

Use the prop label to set the content of the generated <legend> or <label> element (html supported), or by using the named slot label, You may optionally visually hide the label text while still making it available to screen readers by setting the prop label-sr-only.

<b-form-group> will render a <fieldset> with <legend> if the label-for prop is not set. If an input ID is provided to the label-for prop, then a <div> with <label> will be rendered.

If you provide an input id value to the label-for prop (the id must exist on the input contained within the <b-form-group>), a <label> element will be rendered instead of a <legend> element, and will have the for attribute set to the id specified. When specifying the id, do not prepend it with #. The label-for prop should only be used when you have a single form input inside the <b-form-group> component. Do not set the label-for prop when using <b-form-radio-group>, <b-form-checkbox-group>, <b-form-radio>, <b-form-checkbox> or <b-form-file> components, as these inputs include integrated label element(s) and the <legend> element is more suitable.

The label text may also optionally be aligned left, center or right by setting the respective value via the prop label-text-align. Alignment has no effect if label-sr-only is set.

You can also apply additional classes to the label via the label-class prop, such as responsive padding and text alignment utility classes. The label-class prop accepts either a string or array of strings.

Horizontal layout

By default, the label appears above the input element(s), but you may optionally set the prop horizontal to place the label on the same line, and control the width of the label by setting label-cols to the number of columns (default of 3, valid range of 1 through 11). label-cols has no effect if the layout is not horizontal. For viewports below size sm, the label will revert to being displayed above the input control. You can control the breakpoint for this by setting the breakpoint prop ('sm', 'md', 'lg', or 'xl'. The default is 'sm').

<div>
  <b-form-group id="fieldsetHorizontal"
                horizontal
                :label-cols="4"
                breakpoint="md"
                description="Let us know your name."
                label="Enter your name"
                label-for="inputHorizontal">
    <b-form-input id="inputHorizontal"></b-form-input>
  </b-form-group>
</div>

<!-- form-group-horizontal.vue -->

Label size

You can control the label text size match the size of your form input(s) via the optional label-size prop. Values can be 'sm' or 'lg' for small or large label, respectively. Sizes work for both horizontal and non-horizontal form groups.

<div>
  <b-form-group horizontal
                :label-cols="2"
                label-size="sm"
                label="Small"
                label-for="input_sm">
    <b-form-input id="input_sm" size="sm"></b-form-input>
  </b-form-group>
  <b-form-group horizontal
                :label-cols="2"
                label="Default"
                label-for="input_default">
    <b-form-input id="input_default"></b-form-input>
  </b-form-group>
  <b-form-group horizontal
                :label-cols="2"
                label-size="lg"
                label="Large"
                label-for="input_lg">
    <b-form-input id="input_lg" size="lg"></b-form-input>
  </b-form-group>
</div>

<!-- form-group-label-size.vue -->

Description

Optional descriptive text which is always shown with the .text-muted class (html supported) by setting the description prop or using the named slot description. The description text is rendered using the <b-form-text> form sub-component.

Nested form groups

Feel free to nest <b-form-group> components to produce advanced form layouts and semantic grouping of related form controls:

<b-card bg-variant="light">
  <b-form-group horizontal
                breakpoint="lg"
                label="Shipping Address"
                label-size="lg"
                label-class="font-weight-bold pt-0"
                class="mb-0">
    <b-form-group horizontal
                  label="Street:"
                  label-class="text-sm-right"
                  label-for="nestedStreet">
      <b-form-input id="nestedStreet"></b-form-input>
    </b-form-group>
    <b-form-group horizontal
                  label="City:"
                  label-class="text-sm-right"
                  label-for="nestedCity">
      <b-form-input id="nestedCity"></b-form-input>
    </b-form-group>
    <b-form-group horizontal
                  label="State:"
                  label-class="text-sm-right"
                  label-for="nestedState">
      <b-form-input id="nestedState"></b-form-input>
    </b-form-group>
    <b-form-group horizontal
                  label="Country:"
                  label-class="text-sm-right"
                  label-for="nestedCountry">
      <b-form-input id="nestedCountry"></b-form-input>
    </b-form-group>
    <b-form-group horizontal
                  label="Ship via:"
                  label-class="text-sm-right"
                  class="mb-0">
      <b-form-radio-group class="pt-2" :options="['Air', 'Courier', 'Mail']" />
    </b-form-group>
  </b-form-group>
</b-card>

<!-- form-group-nested.vue -->

Validation state feedback

Bootstrap includes validation styles for valid and invalid states on most form controls.

Generally speaking, you’ll want to use a particular state for specific types of feedback:

• 'invalid' is great for when there’s a blocking or required field. A user must fill in this field properly to submit the form.
• 'valid' is ideal for situations when you have per-field validation throughout a form and want to encourage a user through the rest of the fields.
• null Displays no validation state

To apply one of the contextual states on <b-form-group>, set the state prop to 'invalid' (or false), 'valid' (or true), or null. This will programmattically show the apropriate feedback text.

Boostrap V4 uses sibling CSS slectors of :invalid or :valid inputs to show the feedback text. Some form controls (such as checkboxes, radios, and file inputs, or inputs inside input-groups) are wrapped in additional markup that will no longer make the feedback text a sibling of the input, and hence the feedback will not show. In these situations you will ned to set the validity state on the <b-form-group> as well as the input.

Feedback will be shown if the parent <b-form> component does not have the novalidate prop set (or set to false) along with the vadidated prop set (and the input fails or passes native browser validation constraints such as required). Refer to Bootstrap V4's Form component documentation for details on validation methods.

You should always provide content via the invalid-feedback prop (or slot) to aid users using assistive technologies when setting a contextual invalid state.

Invalid feedback

Show optional invalid state feedback text to provide textual state feedback (html supported) by setting the prop invalid-feedback or using the named slot invalid-feedback.

Invalid feedback is rendered using the <b-form-invalid-feedback> form sub-componment.

Note: The prop feedback has been deprecated in favor of the invalid-feedback prop.

Valid feedback

Show optional valid state feedback text to provide textual state feedback (html supported) by setting the prop valid-feedback or using the named slot valid-feedback.

Valid feedback is rendered using the <b-form-valid-feedback> form sub-componment.

Feeback limitations

Note: When using <b-input-group>, <b-form-file>, <b-form-radio-group>, <b-form-radio>, <b-form-checkbox-group> or <b-form-checkbox> inside a <b-form-group>, setting an invalid (or valid) state on the input alone will not trigger the invalid (or valid) feeback to show (due to limitations with the new Bootsrap V4 validation CSS). To get around this, you must also set the invalid/valid state on <b-form-group>. Native browser validation will not trigger the invalid feedback to show when using one of the above mentiond form controls.

Accessibility

To enable auto-generation of aria-* attributes, you should supply a unique id prop to <b-form-group>. This will associate the help text and feeback text to the <b-form-group> and, indirectly to its input control(s).

By default, when no label-for value is provided, <b-form-group> renders the input control(s) inside a an HTML <fieldset> element with the label content placed inside the fieldset's <legend> element. By nature of this markup, the legend content is automatically associated to the containing input control(s).

It is highly recommended that you provide a unique id prop on your input element and set thhe label-for prop to this id, when you have only a single input in the <b-form-group>.

When multiple form controls are placed inside <b-form-group> (i.e. a series or radio or checkbox inputs, or a series of related inputs), do not set the label-for prop, as a label can only be associated with a single input. It is best to use the default rendered markup that produces a <fieldset> + <legend> which will describe the group of inputs.

When placing multiple form controls inside a <b-form-group> (and you are not nesting <b-form-group>components), it is recommended to give each control its own associated <label> (which may be visually hidden using the .sr-only class) and set the label's for attribute to the id of the associated input control. Alternatively, you can set the aria-label attribute on each input control instead of using a <label>. For <b-form-radio> and <b-form-checkbox> (or the group versions), you do not need to set individual labels, as the rendered markup for these types of inputs already includes a <label> element.

Component alias

<b-form-group> can also be used via the alias of <b-form-fieldset>.

Component Reference