Bootstrap4.2 form validation source code analysis and usage

Bootstrap4.2 form validation source code analysis and usage

Comments 0 Comment

How it works

Here’s how form validation works with Bootstrap:

  • HTML form validation is applied via CSS’s two pseudo-classes, :invalid and :valid. It applies to <input>, <select>, and <textarea> elements.
  • Bootstrap scopes the :invalid and :valid styles to parent .was-validated class, usually applied to the <form>. Otherwise, any required field without a value shows up as invalid on page load. This way, you may choose when to activate them (typically after form submission is attempted).
  • To reset the appearance of the form (for instance, in the case of dynamic form submissions using AJAX), remove the .was-validated class from the <form> again after submission.
  • As a fallback, .is-invalid and .is-valid classes may be used instead of the pseudo-classes for server side validation. They do not require a .was-validated parent class.
  • Due to constraints in how CSS works, we cannot (at present) apply styles to a <label> that comes before a form control in the DOM without the help of custom JavaScript.
  • All modern browsers support the constraint validation API, a series of JavaScript methods for validating form controls.
  • Feedback messages may utilize the browser defaults (different for each browser, and unstylable via CSS) or our custom feedback styles with additional HTML and CSS.
  • You may provide custom validity messages with setCustomValidity in JavaScript.

The most important source code for BS4 form validation is the following mixin.

@mixin form-validation-state($state, $color, $icon) {
  .#{$state}-feedback {
    display: none;
    width: 100%;
    margin-top: $form-feedback-margin-top;
    font-size: $form-feedback-font-size;
    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;
    font-size: $form-feedback-tooltip-font-size;
    line-height: $form-feedback-tooltip-line-height;
    color: color-yiq($color);
    background-color: rgba($color, $form-feedback-tooltip-opacity);
    @include border-radius($form-feedback-tooltip-border-radius);
  }

  .form-control {
    .was-validated &:#{$state},
    &.is-#{$state} {
      border-color: $color;

      @if $enable-validation-icons {
        padding-right: $input-height-inner;
        background-image: $icon;
        background-repeat: no-repeat;
        background-position: center right calc(#{$input-height-inner} / 4);
        background-size: calc(#{$input-height-inner} / 2) calc(#{$input-height-inner} / 2);
      }

      &:focus {
        border-color: $color;
        box-shadow: 0 0 0 $input-focus-width rgba($color, .25);
      }

      ~ .#{$state}-feedback,
      ~ .#{$state}-tooltip {
        display: block;
      }
    }
  }

  // stylelint-disable-next-line selector-no-qualifying-type
  textarea.form-control {
    .was-validated &:#{$state},
    &.is-#{$state} {
      @if $enable-validation-icons {
        padding-right: $input-height-inner;
        background-position: top calc(#{$input-height-inner} / 4) right calc(#{$input-height-inner} / 4);
      }
    }
  }

  .custom-select {
    .was-validated &:#{$state},
    &.is-#{$state} {
      border-color: $color;

      @if $enable-validation-icons {
        padding-right: $custom-select-feedback-icon-padding-right;
        background: $custom-select-background, $icon $custom-select-bg no-repeat $custom-select-feedback-icon-position / $custom-select-feedback-icon-size;
      }

      &:focus {
        border-color: $color;
        box-shadow: 0 0 0 $input-focus-width rgba($color, .25);
      }

      ~ .#{$state}-feedback,
      ~ .#{$state}-tooltip {
        display: block;
      }
    }
  }


  .form-control-file {
    .was-validated &:#{$state},
    &.is-#{$state} {
      ~ .#{$state}-feedback,
      ~ .#{$state}-tooltip {
        display: block;
      }
    }
  }

  .form-check-input {
    .was-validated &:#{$state},
    &.is-#{$state} {
      ~ .form-check-label {
        color: $color;
      }

      ~ .#{$state}-feedback,
      ~ .#{$state}-tooltip {
        display: block;
      }
    }
  }

  .custom-control-input {
    .was-validated &:#{$state},
    &.is-#{$state} {
      ~ .custom-control-label {
        color: $color;

        &::before {
          border-color: $color;
        }
      }

      ~ .#{$state}-feedback,
      ~ .#{$state}-tooltip {
        display: block;
      }

      &:checked {
        ~ .custom-control-label::before {
          border-color: lighten($color, 10%);
          @include gradient-bg(lighten($color, 10%));
        }
      }

      &:focus {
        ~ .custom-control-label::before {
          box-shadow: 0 0 0 $input-focus-width rgba($color, .25);
        }

        &:not(:checked) ~ .custom-control-label::before {
          border-color: $color;
        }
      }
    }
  }

  // custom file
  .custom-file-input {
    .was-validated &:#{$state},
    &.is-#{$state} {
      ~ .custom-file-label {
        border-color: $color;
      }

      ~ .#{$state}-feedback,
      ~ .#{$state}-tooltip {
        display: block;
      }

      &:focus {
        ~ .custom-file-label {
          border-color: $color;
          box-shadow: 0 0 0 $input-focus-width rgba($color, .25);
        }
      }
    }
  }
}

The compiled CSS would be much clearer and self-explanatory.

.valid-feedback {
  display: none;
  width: 100%;
  margin-top: 0.25rem;
  font-size: 80%;
  color: #28a745;
}

.valid-tooltip {
  position: absolute;
  top: 100%;
  z-index: 5;
  display: none;
  max-width: 100%;
  padding: 0.25rem 0.5rem;
  margin-top: .1rem;
  font-size: 0.875rem;
  line-height: 1.5;
  color: #fff;
  background-color: rgba(40, 167, 69, 0.9);
  border-radius: 0.25rem;
}

.was-validated .form-control:valid, .form-control.is-valid {
  border-color: #28a745;
  padding-right: 2.25rem;
  background-image: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 8 8'%3e%3cpath fill='%2328a745' 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'/%3e%3c/svg%3e");
  background-repeat: no-repeat;
  background-position: center right calc(2.25rem / 4);
  background-size: calc(2.25rem / 2) calc(2.25rem / 2);
}

.was-validated .form-control:valid:focus, .form-control.is-valid:focus {
  border-color: #28a745;
  box-shadow: 0 0 0 0.2rem rgba(40, 167, 69, 0.25);
}

.was-validated .form-control:valid ~ .valid-feedback,
.was-validated .form-control:valid ~ .valid-tooltip, .form-control.is-valid ~ .valid-feedback,
.form-control.is-valid ~ .valid-tooltip {
  display: block;
}

.was-validated textarea.form-control:valid, textarea.form-control.is-valid {
  padding-right: 2.25rem;
  background-position: top calc(2.25rem / 4) right calc(2.25rem / 4);
}

.was-validated .custom-select:valid, .custom-select.is-valid {
  border-color: #28a745;
  padding-right: 3.4375rem;
  background: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 4 5'%3e%3cpath fill='%23343a40' d='M2 0L0 2h4zm0 5L0 3h4z'/%3e%3c/svg%3e") no-repeat right 0.75rem center/8px 10px, url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 8 8'%3e%3cpath fill='%2328a745' 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'/%3e%3c/svg%3e") #fff no-repeat center right 1.75rem/1.125rem 1.125rem;
}

.was-validated .custom-select:valid:focus, .custom-select.is-valid:focus {
  border-color: #28a745;
  box-shadow: 0 0 0 0.2rem rgba(40, 167, 69, 0.25);
}

.was-validated .custom-select:valid ~ .valid-feedback,
.was-validated .custom-select:valid ~ .valid-tooltip, .custom-select.is-valid ~ .valid-feedback,
.custom-select.is-valid ~ .valid-tooltip {
  display: block;
}

.was-validated .form-control-file:valid ~ .valid-feedback,
.was-validated .form-control-file:valid ~ .valid-tooltip, .form-control-file.is-valid ~ .valid-feedback,
.form-control-file.is-valid ~ .valid-tooltip {
  display: block;
}

.was-validated .form-check-input:valid ~ .form-check-label, .form-check-input.is-valid ~ .form-check-label {
  color: #28a745;
}

.was-validated .form-check-input:valid ~ .valid-feedback,
.was-validated .form-check-input:valid ~ .valid-tooltip, .form-check-input.is-valid ~ .valid-feedback,
.form-check-input.is-valid ~ .valid-tooltip {
  display: block;
}

.was-validated .custom-control-input:valid ~ .custom-control-label, .custom-control-input.is-valid ~ .custom-control-label {
  color: #28a745;
}

.was-validated .custom-control-input:valid ~ .custom-control-label::before, .custom-control-input.is-valid ~ .custom-control-label::before {
  border-color: #28a745;
}

.was-validated .custom-control-input:valid ~ .valid-feedback,
.was-validated .custom-control-input:valid ~ .valid-tooltip, .custom-control-input.is-valid ~ .valid-feedback,
.custom-control-input.is-valid ~ .valid-tooltip {
  display: block;
}

.was-validated .custom-control-input:valid:checked ~ .custom-control-label::before, .custom-control-input.is-valid:checked ~ .custom-control-label::before {
  border-color: #34ce57;
  background-color: #34ce57;
}

.was-validated .custom-control-input:valid:focus ~ .custom-control-label::before, .custom-control-input.is-valid:focus ~ .custom-control-label::before {
  box-shadow: 0 0 0 0.2rem rgba(40, 167, 69, 0.25);
}

.was-validated .custom-control-input:valid:focus:not(:checked) ~ .custom-control-label::before, .custom-control-input.is-valid:focus:not(:checked) ~ .custom-control-label::before {
  border-color: #28a745;
}

.was-validated .custom-file-input:valid ~ .custom-file-label, .custom-file-input.is-valid ~ .custom-file-label {
  border-color: #28a745;
}

.was-validated .custom-file-input:valid ~ .valid-feedback,
.was-validated .custom-file-input:valid ~ .valid-tooltip, .custom-file-input.is-valid ~ .valid-feedback,
.custom-file-input.is-valid ~ .valid-tooltip {
  display: block;
}

.was-validated .custom-file-input:valid:focus ~ .custom-file-label, .custom-file-input.is-valid:focus ~ .custom-file-label {
  border-color: #28a745;
  box-shadow: 0 0 0 0.2rem rgba(40, 167, 69, 0.25);
}

.invalid-feedback {
  display: none;
  width: 100%;
  margin-top: 0.25rem;
  font-size: 80%;
  color: #dc3545;
}

.invalid-tooltip {
  position: absolute;
  top: 100%;
  z-index: 5;
  display: none;
  max-width: 100%;
  padding: 0.25rem 0.5rem;
  margin-top: .1rem;
  font-size: 0.875rem;
  line-height: 1.5;
  color: #fff;
  background-color: rgba(220, 53, 69, 0.9);
  border-radius: 0.25rem;
}

.was-validated .form-control:invalid, .form-control.is-invalid {
  border-color: #dc3545;
  padding-right: 2.25rem;
  background-image: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' fill='%23dc3545' viewBox='-2 -2 7 7'%3e%3cpath stroke='%23dc3545' d='M0 0l3 3m0-3L0 3'/%3e%3ccircle r='.5'/%3e%3ccircle cx='3' r='.5'/%3e%3ccircle cy='3' r='.5'/%3e%3ccircle cx='3' cy='3' r='.5'/%3e%3c/svg%3E");
  background-repeat: no-repeat;
  background-position: center right calc(2.25rem / 4);
  background-size: calc(2.25rem / 2) calc(2.25rem / 2);
}

.was-validated .form-control:invalid:focus, .form-control.is-invalid:focus {
  border-color: #dc3545;
  box-shadow: 0 0 0 0.2rem rgba(220, 53, 69, 0.25);
}

.was-validated .form-control:invalid ~ .invalid-feedback,
.was-validated .form-control:invalid ~ .invalid-tooltip, .form-control.is-invalid ~ .invalid-feedback,
.form-control.is-invalid ~ .invalid-tooltip {
  display: block;
}

.was-validated textarea.form-control:invalid, textarea.form-control.is-invalid {
  padding-right: 2.25rem;
  background-position: top calc(2.25rem / 4) right calc(2.25rem / 4);
}

.was-validated .custom-select:invalid, .custom-select.is-invalid {
  border-color: #dc3545;
  padding-right: 3.4375rem;
  background: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 4 5'%3e%3cpath fill='%23343a40' d='M2 0L0 2h4zm0 5L0 3h4z'/%3e%3c/svg%3e") no-repeat right 0.75rem center/8px 10px, url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' fill='%23dc3545' viewBox='-2 -2 7 7'%3e%3cpath stroke='%23dc3545' d='M0 0l3 3m0-3L0 3'/%3e%3ccircle r='.5'/%3e%3ccircle cx='3' r='.5'/%3e%3ccircle cy='3' r='.5'/%3e%3ccircle cx='3' cy='3' r='.5'/%3e%3c/svg%3E") #fff no-repeat center right 1.75rem/1.125rem 1.125rem;
}

.was-validated .custom-select:invalid:focus, .custom-select.is-invalid:focus {
  border-color: #dc3545;
  box-shadow: 0 0 0 0.2rem rgba(220, 53, 69, 0.25);
}

.was-validated .custom-select:invalid ~ .invalid-feedback,
.was-validated .custom-select:invalid ~ .invalid-tooltip, .custom-select.is-invalid ~ .invalid-feedback,
.custom-select.is-invalid ~ .invalid-tooltip {
  display: block;
}

.was-validated .form-control-file:invalid ~ .invalid-feedback,
.was-validated .form-control-file:invalid ~ .invalid-tooltip, .form-control-file.is-invalid ~ .invalid-feedback,
.form-control-file.is-invalid ~ .invalid-tooltip {
  display: block;
}

.was-validated .form-check-input:invalid ~ .form-check-label, .form-check-input.is-invalid ~ .form-check-label {
  color: #dc3545;
}

.was-validated .form-check-input:invalid ~ .invalid-feedback,
.was-validated .form-check-input:invalid ~ .invalid-tooltip, .form-check-input.is-invalid ~ .invalid-feedback,
.form-check-input.is-invalid ~ .invalid-tooltip {
  display: block;
}

.was-validated .custom-control-input:invalid ~ .custom-control-label, .custom-control-input.is-invalid ~ .custom-control-label {
  color: #dc3545;
}

.was-validated .custom-control-input:invalid ~ .custom-control-label::before, .custom-control-input.is-invalid ~ .custom-control-label::before {
  border-color: #dc3545;
}

.was-validated .custom-control-input:invalid ~ .invalid-feedback,
.was-validated .custom-control-input:invalid ~ .invalid-tooltip, .custom-control-input.is-invalid ~ .invalid-feedback,
.custom-control-input.is-invalid ~ .invalid-tooltip {
  display: block;
}

.was-validated .custom-control-input:invalid:checked ~ .custom-control-label::before, .custom-control-input.is-invalid:checked ~ .custom-control-label::before {
  border-color: #e4606d;
  background-color: #e4606d;
}

.was-validated .custom-control-input:invalid:focus ~ .custom-control-label::before, .custom-control-input.is-invalid:focus ~ .custom-control-label::before {
  box-shadow: 0 0 0 0.2rem rgba(220, 53, 69, 0.25);
}

.was-validated .custom-control-input:invalid:focus:not(:checked) ~ .custom-control-label::before, .custom-control-input.is-invalid:focus:not(:checked) ~ .custom-control-label::before {
  border-color: #dc3545;
}

.was-validated .custom-file-input:invalid ~ .custom-file-label, .custom-file-input.is-invalid ~ .custom-file-label {
  border-color: #dc3545;
}

.was-validated .custom-file-input:invalid ~ .invalid-feedback,
.was-validated .custom-file-input:invalid ~ .invalid-tooltip, .custom-file-input.is-invalid ~ .invalid-feedback,
.custom-file-input.is-invalid ~ .invalid-tooltip {
  display: block;
}

.was-validated .custom-file-input:invalid:focus ~ .custom-file-label, .custom-file-input.is-invalid:focus ~ .custom-file-label {
  border-color: #dc3545;
  box-shadow: 0 0 0 0.2rem rgba(220, 53, 69, 0.25);

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.