Hướng dẫn bootstrap 3 form validation
Examples and usage guidelines for form control styles, layout options, and custom components for creating a wide variety of forms.
Overview
Bootstrap’s form controls expand on our Rebooted form styles with classes. Use these classes to opt into their customized displays for a more consistent rendering across browsers and devices.
Be sure to use an
appropriate type attribute on all inputs [e.g., email for email address or number for numerical information] to take advantage of newer input controls like email verification, number selection, and more.
Here’s a quick example to demonstrate Bootstrap’s form styles. Keep reading for documentation on required classes, form layout, and more.
Email address
We'll never share your email with anyone else.
Password
Check me out
Submit
Form controls
Textual form controls—like .form-control class. Included are styles for general appearance, focus state, sizing, and more.
Be sure to explore our custom forms to further style
Email address
Example select
Example multiple select
Example textarea
Email address
Example select
1
2
3
4
5
Example multiple select
1
2
3
4
5
Example textarea
For file inputs, swap the .form-control for .form-control-file.
Example file input
Sizing
Set heights using classes like .form-control-lg and .form-control-sm.
Large select
Default select
Small select
Readonly
Add the readonly boolean attribute on an input to prevent modification of the input’s value. Read-only inputs appear lighter [just like disabled inputs], but retain the standard
cursor.
Readonly plain text
If you want to have .form-control-plaintext class to remove the default form field styling and preserve the correct margin and padding.
Email
Password
Email
Password
Confirm identity
Checkboxes and radios
Default checkboxes and radios are improved upon with the help of .form-check, a single class for both input types that improves
the layout and behavior of their HTML elements. Checkboxes are for selecting one or several options in a list, while radios are for selecting one option from many.
Disabled checkboxes and radios are supported, but to provide a not-allowed cursor on hover of the parent disabled attribute to the .form-check-input. The disabled attribute will apply a lighter color to help indicate the input’s state.
Checkboxes and radios use are built to support HTML-based
form validation and provide concise, accessible labels. As such, our id and for attributes to relate the
Default [stacked]
By default, any number of checkboxes and radios that are immediate sibling will be vertically stacked and appropriately spaced with .form-check.
Default checkbox
Disabled checkbox
Default checkbox
Disabled checkbox
Default radio
Second default radio
Disabled radio
Default radio
Second default radio
Disabled radio
Inline
Group checkboxes or radios on the same horizontal row by adding .form-check-inline to any .form-check.
1
2
3 [disabled]
1
2
3 [disabled]
Without labels
Add .position-static to inputs within .form-check that don’t have any label text. Remember to still provide some form of label for assistive technologies [for instance, using aria-label].
Layout
Since Bootstrap applies display: block and width: 100% to almost all our form controls, forms will by default stack vertically. Additional classes can be used to vary this layout on a per-form basis.
Form groups
The .form-group class is the easiest way to add some structure to forms. It provides a flexible class that encourages proper grouping of labels, controls, optional help text, and form validation messaging. By default it only applies margin-bottom, but it picks up additional styles in .form-inline as needed. Use it with s, or nearly any other element.
Example label
Form grid
More complex forms can be built using our grid
classes. Use these for form layouts that require multiple columns, varied widths, and additional alignment options.
Form row
You may also swap .row for .form-row, a variation of our standard grid row that overrides the default column gutters for tighter and more compact layouts.
More complex layouts can also be created with the grid system.
Email
Password
Address
Address 2
City
State
Choose...
...
Zip
Check me out
Sign in
Horizontal form
Create
horizontal forms with the grid by adding the .row class to form groups and using the .col-*-* classes to specify the width of your labels and controls. Be sure to add .col-form-label to your
At times, you maybe need to use margin or padding utilities to create that perfect alignment you need. For example, we’ve removed the padding-top on our stacked radio inputs label to better align the text baseline.
Email
Password
Radios
First radio
Second radio
Third disabled radio
Checkbox
Example checkbox
Sign in
Horizontal form label sizingBe sure to use .col-form-label-sm or .col-form-label-lg to your .form-control-lg and .form-control-sm.
Email
Email
Email
Column sizing
As shown in the previous examples, our grid system allows you to place any number of .cols within a .row or .form-row. They’ll split the available width equally between them. You may also pick a subset of your columns to
take up more or less space, while the remaining .cols equally split the rest, with specific column classes like .col-7.
Auto-sizing
The example below uses a flexbox utility to vertically center the contents and changes .col to .col-auto so that your columns only take up as much space as needed. Put another way, the column sizes itself based on the contents.
Name
Username
@
Remember me
Submit
You can then remix that once again with size-specific
column classes.
Name
Username
@
Remember me
Submit
And of course custom form controls are supported.
Preference
Choose...
One
Two
Three
Remember my preference
Submit
Inline forms
Use the .form-inline class to display a series of labels, form controls, and buttons on a single horizontal row. Form controls within inline forms vary slightly from their default states.
- Controls are
display: flex, collapsing any HTML white space
and allowing you to provide alignment control with spacing and flexbox utilities. - Controls and input groups receive
width: auto to override the Bootstrap default width: 100%. - Controls only appear inline in viewports that are at least 576px wide to account for narrow viewports on mobile devices.
You
may need to manually address the width and alignment of individual form controls with spacing utilities [as shown below]. Lastly, be sure to always include a .sr-only.
Name
Username
@
Remember me
Submit
Custom form controls and selects are also supported.
Preference
Choose...
One
Two
Three
Remember my preference
Submit
Alternatives
to hidden labels
Assistive technologies such as screen readers will have trouble with your forms if you don’t include a label for every input. For these inline forms, you can hide the labels using the .sr-only class. There are further alternative methods of providing a label for assistive technologies, such as the aria-label, aria-labelledby or title attribute. If none of these are present, assistive technologies may resort to using the placeholder attribute, if present, but note that use of
placeholder as a replacement for other labelling methods is not advised.
Help text
Block-level help text in forms can be created using .form-text [previously known as .help-block in v3]. Inline help text can be flexibly implemented using any inline HTML element and utility classes like .text-muted.
Associating help text with form controls
Help text should be explicitly associated with the
form control it relates to using the aria-describedby attribute. This will ensure that assistive technologies—such as screen readers—will announce this help text when the user focuses or enters the control.
Help text below inputs can be styled with .form-text. This class includes display: block and adds some top margin for easy spacing from the inputs above.
Password Your password must be 8-20 characters long, contain letters
and numbers, and must not contain spaces, special characters, or emoji.
Password
Your password must be 8-20 characters long, contain letters and numbers, and must not contain spaces, special characters, or emoji.
Inline text can use any typical inline HTML element [be it a
Password
Must be 8-20 characters long.
Disabled forms
Add the disabled boolean attribute on an input to prevent user interactions and make it appear lighter.
Add the disabled attribute to a
Disabled input
Disabled select menu
Disabled select
Can't check this
Submit
Caveat with anchors
By default, browsers will treat all native form controls [pointer-events: none. As noted in the section about
disabled state for buttons [and specifically in the sub-section for anchor elements], this CSS property is not yet standardized and isn’t fully supported in Opera 18 and below, or in Internet Explorer 10, and won’t prevent keyboard users from being able to focus or activate these links. So to be safe, use custom JavaScript to disable such links.
Cross-browser
compatibility
While Bootstrap will apply these styles in all browsers, Internet Explorer 11 and below don’t fully support the disabled attribute on a
Validation
Provide valuable, actionable feedback to your users with HTML5 form validation–available in all our supported browsers. Choose from the browser
default validation feedback, or implement custom messages with our built-in classes and starter JavaScript.
We highly recommend custom validation styles as native browser defaults are not announced to screen readers.
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 - Bootstrap
scopes the
:invalid and :valid styles to parent .was-validated class, usually applied to the - 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
- 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.
With that in mind, consider the following demos for our custom form validation styles, optional server side classes, and browser defaults.
Custom styles
For custom Bootstrap form validation messages, you’ll need to add the novalidate boolean attribute to your
When attempting to submit, you’ll see the :invalid and :valid styles applied to your form controls.
First name
Looks good!
Last name
Looks good!
Username
@
Please choose a username.
City
Please provide a valid city.
State
Please provide a valid state.
Zip
Please provide a valid zip.
Agree to terms and conditions
You must agree before submitting.
Submit form
// Example starter JavaScript for disabling form submissions if there are invalid fields
[function[] {
'use strict';
window.addEventListener['load', function[] {
// Fetch all the forms we want to apply custom Bootstrap validation styles to
var forms = document.getElementsByClassName['needs-validation'];
// Loop over them and prevent submission
var validation = Array.prototype.filter.call[forms, function[form] {
form.addEventListener['submit', function[event] {
if [form.checkValidity[] === false] {
event.preventDefault[];
event.stopPropagation[];
}
form.classList.add['was-validated'];
}, false];
}];
}, false];
}][];
Browser
defaults
Not interested in custom validation feedback messages or writing JavaScript to change form behaviors? All good, you can use the browser defaults. Try submitting the form below. Depending on your browser and OS, you’ll see a slightly different style of feedback.
While these feedback styles cannot be styled with CSS, you can still customize the feedback text through JavaScript.
First name
Last name
Username
@
City
State
Zip
Agree to terms and conditions
Submit form
Server side
We recommend using client side
validation, but in case you require server side, you can indicate invalid and valid form fields with .is-invalid and .is-valid. Note that .invalid-feedback is also supported with these classes.
First name
Looks good!
Last name
Looks good!
Username
@
Please choose a username.
City
Please provide a valid city.
State
Please provide a valid state.
Zip
Please provide a valid zip.
Agree to terms and conditions
You must agree before submitting.
Submit form
Supported elements
Our example forms show native textual
Check this custom checkbox
Example invalid feedback text
Toggle this custom radio
Or toggle this other custom radio
More example invalid feedback text
Open this select menu
One
Two
Three
Example invalid custom select feedback
Choose file...
Example invalid custom file feedback
Tooltips
If your form layout allows it, you can swap the .{valid|invalid}-feedback
classes for .{valid|invalid}-tooltip classes to display validation feedback in a styled tooltip. Be sure to have a parent with position: relative on it for tooltip positioning. In the example below, our column classes have this already, but your project may require an alternative setup.
First name
Looks good!
Last name
Looks good!
Username
@
Please choose a unique and valid username.
City
Please provide a valid city.
State
Please provide a valid state.
Zip
Please provide a valid zip.
Submit form
Custom forms
For even more customization and cross browser consistency, use our completely custom form elements to replace the browser defaults. They’re built on top of semantic and
accessible markup, so they’re solid replacements for any default form control.
Checkboxes and radios
Each checkbox and radio is wrapped in a with a sibling
to create our custom control and a
for the accompanying text. Structurally, this is the same approach as our default
.form-check.
We use the sibling selector [~] for all our :checked—to properly style our custom form indicator. When combined
with the .custom-control-label class, we can also style the text for each item based on the
We hide the default opacity and use the .custom-control-label to build a new custom form indicator in its place with ::before and ::after. Unfortunately we can’t build a custom one from just the content doesn’t work on that element.
In the checked states, we use base64 embedded SVG icons from
Open Iconic. This provides us the best control for styling and positioning across browsers and devices.
Checkboxes
Check this custom checkbox
Check this custom checkbox
Custom checkboxes can also utilize the :indeterminate pseudo class when manually set via JavaScript [there is no available HTML attribute for specifying it].
Check this
custom checkbox
If you’re using jQuery, something like this should suffice:
$['.your-checkbox'].prop['indeterminate', true]
Radios
Toggle this custom radio
Or toggle this other custom radio
Toggle this custom radio
Or toggle this other custom radio
Inline
Toggle this custom radio
Or toggle this other custom
radio
Toggle this custom radio
Or toggle this other custom radio
Disabled
Custom checkboxes and radios can also be disabled. Add the disabled boolean attribute to the
Check this custom checkbox
Toggle this custom radio
Check this custom checkbox
Toggle this custom radio
Custom .custom-select to
trigger the custom styles.
Open this select menu
One
Two
Three
You may also choose from small and large custom selects to match our similarly sized text inputs.
Open this select menu
One
Two
Three
Open this select menu
One
Two
Three
The multiple attribute is also supported:
Open this select menu
One
Two
Three
As is the size attribute:
Open this select menu
One
Two
Three
File browser
The file input is the most gnarly of the bunch and requires additional JavaScript if you’d like to hook them up with functional Choose file… and selected file
name text.
Choose file
We hide the default file opacity and instead style the ::after. Lastly, we declare a width and height on the
Translating or customizing the strings
The :lang[] pseudo-class is used to allow for
translation of the “Browse” text into other languages. Override or add entries to the $custom-file-text Sass variable with the relevant language tag and localized strings. The English strings can be customized the same way. For example, here’s how one might add a Spanish translation [Spanish’s language code is es]:
$custom-file-text: [
en: "Browse",
es: "Elegir"
];
Here’s lang[es] in action on the custom file input for a Spanish
translation:
Seleccionar Archivo
You’ll need to set the language of your document [or subtree thereof] correctly in order for the correct text to be shown. This can be done using the lang attribute on the Content-Language HTTP header, among other methods.