Bootstrap 4是整个项目的重大改写。下面总结了最显着的变化，随后对相关组件进行了更具体的更改。

Beta 2的变化

While in beta, we aim to have no breaking changes. However, things don’t always go as planned. Below are the breaking changes to bear in mind when moving from Beta 1 to Beta 2.

Breaking

• Removed $badge-color variable and its usage on .badge. We use a color contrast function to pick a color based on the background-color, so the variable is unnecessary.

• Renamed grayscale() function to gray() to avoid breaking conflict with the CSS native grayscale filter.

• Renamed .table-inverse, .thead-inverse, and .thead-default to .*-dark and .*-light, matching our color schemes used elsewhere.

• Responsive tables now generate classes for each grid breakpoint. This breaks from Beta 1 in that the .table-responsive you’ve been using is more like .table-responsive-md. You may now use .table-responsive or .table-responsive-{sm,md,lg,xl} as needed.

• Dropped Bower support as the package manager has been deprecated for alternatives (e.g., Yarn or npm). See bower/bower#2298 for details.

• Bootstrap still requires jQuery 1.9.1 or higher, but you’re advised to use version 3.x since v3.x’s supported browsers are the ones Bootstrap supports plus v3.x has some security fixes.

• Removed the unused .form-control-label class. If you did make use of this class, it was duplicate of the .col-form-label class that vertically centered a <label> with it’s associated input in horizontal form layouts.

• Changed the color-yiq from a mixin that included the color property to a function that returns a value, allowing you to use it for any CSS property. For example, instead of color-yiq(#000), you’d write color: color-yiq(#000);.

Highlights

• Introduced new pointer-events usage on modals. The outer .modal-dialog passes through events with pointer-events: none for custom click handling (making it possible to just listen on the .modal-backdrop for any clicks), and then counteracts it for the actual .modal-content with pointer-events: auto.

Summary

Here are the big ticket items you’ll want to be aware of when moving from v3 to v4.

Browser support

• Dropped IE8, IE9, and iOS 6 support. v4 is now only IE10+ and iOS 7+. For sites needing either of those, use v3.

• Added official support for Android v5.0 Lollipop’s Browser and WebView. Earlier versions of the Android Browser and WebView remain only unofficially supported.

Global changes

• Flexbox is enabled by default. In general this means a move away from floats and more across our components.

• Switched from Less to Sass for our source CSS files.

• Switched from px to rem as our primary CSS unit, though pixels are still used for media queries and grid behavior as device viewports are not affected by type size.

• Global font-size increased from 14px to 16px.

• Revamped grid tiers to add a fifth option (addressing smaller devices at 576px and below) and removed the -xs infix from those classes. Example: .col-6.col-sm-4.col-md-3.

• Replaced the separate optional theme with configurable options via SCSS variables (e.g., $enable-gradients: true).

• Build system overhauled to use a series of npm scripts instead of Grunt. See package.json for all scripts, or our project readme for local development needs.

• Non-responsive usage of Bootstrap is no longer supported.

• Dropped the online Customizer in favor of more extensive setup documentation and customized builds.

• Added dozens of new utility classes for common CSS property-value pairs and margin/padding spacing shortcuts.

Grid system

• Moved to flexbox.

• Added support for flexbox in the grid mixins and predefined classes.

• As part of flexbox, included support for vertical and horizontal alignment classes.

• Updated grid class names and a new grid tier.

• Added a new sm grid tier below 768px for more granular control. We now have xs, sm, md, lg, and xl. This also means every tier has been bumped up one level (so .col-md-6 in v3 is now .col-lg-6 in v4).

• xs grid classes have been modified to not require the infix to more accurately represent that they start applying styles at min-width: 0 and not a set pixel value. Instead of .col-xs-6, it’s now .col-6. All other grid tiers require the infix (e.g., sm).

• Updated grid sizes, mixins, and variables.

• Grid gutters now have a Sass map so you can specify specific gutter widths at each breakpoint.

• Updated grid mixins to utilize a make-col-ready prep mixin and a make-col to set the flex and max-width for individual column sizing.

• Changed grid system media query breakpoints and container widths to account for new grid tier and ensure columns are evenly divisible by 12 at their max width.

• Grid breakpoints and container widths are now handled via Sass maps ($grid-breakpoints and $container-max-widths) instead of a handful of separate variables. These replace the @screen-* variables entirely and allow you to fully customize the grid tiers.

• Media queries have also changed. Instead of repeating our media query declarations with the same value each time, we now have @include media-breakpoint-up/down/only. Now, instead of writing @media (min-width: @screen-sm-min) { ... }, you can write @include media-breakpoint-up(sm) { ... }.

Components

• Dropped panels, thumbnails, and wells for a new all-encompassing component, cards.

• Dropped the Glyphicons icon font. If you need icons, some options are:

• the upstream version of Glyphicons

• Octicons

• Font Awesome

• See the Extend page for a list of alternatives. Have additional suggestions? Please open an issue or PR.

• Dropped the Affix jQuery plugin.

• We recommend using position: sticky instead. See the HTML5 Please entry for details and specific polyfill recommendations. One suggestion is to use an @supports rule for implementing it (e.g., @supports (position: sticky) { ... })/

• If you were using Affix to apply additional, non-position styles, the polyfills might not support your use case. One option for such uses is the third-party ScrollPos-Styler library.

• Dropped the pager component as it was essentially slightly customized buttons.

• Refactored nearly all components to use more un-nested class selectors instead of over-specific children selectors.

By component

This list highlights key changes by component between v3.x.x and v4.0.0.

Reboot

New to Bootstrap 4 is the Reboot, a new stylesheet that builds on Normalize with our own somewhat opinionated reset styles. Selectors appearing in this file only use elements—there are no classes here. This isolates our reset styles from our component styles for a more modular approach. Some of the most important resets this includes are the box-sizing: border-box change, moving from em to rem units on many elements, link styles, and many form element resets.

Typography

• Moved all .text- utilities to the _utilities.scss file.

• Dropped .page-header as, aside from the border, all its styles can be applied via utilities.

• .dl-horizontal has been dropped. Instead, use .row on <dl> and use grid column classes (or mixins) on its <dt> and <dd> children.

• Custom <blockquote> styling has moved to classes—.blockquote and the .blockquote-reverse modifier.

• .list-inline now requires that its children list items have the new .list-inline-item class applied to them.

Images

• Renamed .img-responsive to .img-fluid.

• Renamed .img-rounded to .rounded

• Renamed .img-circle to .rounded-circle

Tables

• Nearly all instances of the > selector have been removed, meaning nested tables will now automatically inherit styles from their parents. This greatly simplifies our selectors and potential customizations.

• Responsive tables no longer require a wrapping element. Instead, just put the .table-responsive right on the <table>.

• Renamed .table-condensed to .table-sm for consistency.

• Added a new .table-inverse option.

• Added table header modifiers: .thead-default and .thead-inverse.

• Renamed contextual classes to have a .table--prefix. Hence .active, .success, .warning, .danger and .info to .table-active, .table-success, .table-warning, .table-danger and .table-info.

Forms

• Moved element resets to the _reboot.scss file.

• Renamed .control-label to .col-form-label.

• Renamed .input-lg and .input-sm to .form-control-lg and .form-control-sm, respectively.

• Dropped .form-group-* classes for simplicity’s sake. Use .form-control-* classes instead now.

• Dropped .help-block and replaced it with .form-text for block-level help text. For inline help text and other flexible options, use utility classes like .text-muted.

• Dropped .radio-inline and .checkbox-inline.

• Consolidated .checkbox and .radio into .form-check and the various .form-check-* classes.

• Horizontal forms overhauled:

• Dropped the .form-horizontal class requirement.

• .form-group no longer applies styles from the .row via mixin, so .row is now required for horizontal grid layouts (e.g., <div class="form-group row">).

• Added new .col-form-label class to vertically center labels with .form-controls.

• Added new .form-row for compact form layouts with the grid classes (swap your .row for a .form-row and go).

• Added custom forms support (for checkboxes, radios, selects, and file inputs).

• Replaced .has-error, .has-warning, and .has-success classes with HTML5 form validation via CSS’s :invalid and :valid pseudo-classes.

• Renamed .form-control-static to .form-control-plaintext.

Buttons

• Renamed .btn-default to .btn-secondary.

• Dropped the .btn-xs class entirely as .btn-sm is proportionally much smaller than v3’s.

• The stateful button feature of the button.js jQuery plugin has been dropped. This includes the $().button(string) and $().button('reset') methods. We advise using a tiny bit of custom JavaScript instead, which will have the benefit of behaving exactly the way you want it to.

• Note that the other features of the plugin (button checkboxes, button radios, single-toggle buttons) have been retained in v4.

• Change buttons’ [disabled] to :disabled as IE9+ supports :disabled. However fieldset[disabled] is still necessary because native disabled fieldsets are still buggy in IE11.

Button group

• Rewrote component with flexbox.

• Removed .btn-group-justified. As a replacement you can use <div class="btn-group d-flex" role="group"></div> as a wrapper around elements with .w-100.

• Dropped the .btn-group-xs class entirely given removal of .btn-xs.

• Removed explicit spacing between button groups in button toolbars; use margin utilities now.

• Improved documentation for use with other components.

Dropdowns

• Switched from parent selectors to singular classes for all components, modifiers, etc.

• Simplified dropdown styles to no longer ship with upward or downward facing arrows attached to the dropdown menu.

• Dropdowns can be built with <div>s or <ul>s now.

• Rebuilt dropdown styles and markup to provide easy, built-in support for <a> and <button> based dropdown items.

• Renamed .divider to .dropdown-divider.

• Dropdown items now require .dropdown-item.

• Dropdown toggles no longer require an explicit <span class="caret"></span>; this is now provided automatically via CSS’s ::after on .dropdown-toggle.

Grid system

• Added a new 576px grid breakpoint as sm, meaning there are now five total tiers (xs, sm, md, lg, and xl).

• Renamed the responsive grid modifier classes from .col-{breakpoint}-{modifier}-{size} to .{modifier}-{breakpoint}-{size} for simpler grid classes.

• Dropped push and pull modifier classes for the new flexbox-powered order classes. For example, instead of .col-8.push-4 and .col-4.pull-8, you’d use .col-8.order-2 and .col-4.order-1.

• Added flexbox utility classes for grid system and components.

List groups

• Rewrote component with flexbox.

• Replaced a.list-group-item with an explicit class, .list-group-item-action, for styling link and button versions of list group items.

• Added .list-group-flush class for use with cards.

Modal

• Rewrote component with flexbox.

• Given move to flexbox, alignment of dismiss icons in the header is likely broken as we’re no longer using floats. Floated content comes first, but with flexbox that’s no longer the case. Update your dismiss icons to come after modal titles to fix.

• The remote option (which could be used to automatically load and inject external content into a modal) and the corresponding loaded.bs.modal event were removed. We recommend instead using client-side templating or a data binding framework, or calling jQuery.load yourself.

Navs

• Rewrote component with flexbox.

• Dropped nearly all > selectors for simpler styling via un-nested classes.

• Instead of HTML-specific selectors like .nav > li > a, we use separate classes for .navs, .nav-items, and .nav-links. This makes your HTML more flexible while bringing along increased extensibility.

Navbar

The navbar has been entirely rewritten in flexbox with improved support for alignment, responsiveness, and customization.

• Responsive navbar behaviors are now applied to the .navbar class via the required .navbar-expand-{breakpoint} where you choose where to collapse the navbar. Previously this was a Less variable modification and required recompiling.

• .navbar-default is now .navbar-light, though .navbar-dark remains the same. One of these is required on each navbar. However, these classes no longer set background-colors; instead they essentially only affect color.

• Navbars now require a background declaration of some kind. Choose from our background utilities (.bg-*) or set your own with the light/inverse classes above for mad customization.

• Given flexbox styles, navbars can now use flexbox utilities for easy alignment options.

• .navbar-toggle is now .navbar-toggler and has different styles and inner markup (no more three <span>s).

• Dropped the .navbar-form class entirely. It’s no longer necessary; instead, just use .form-inline and apply margin utilities as necessary.

• Navbars no longer include margin-bottom or border-radius by default. Use utilities as necessary.

• All examples featuring navbars have been updated to include new markup.

Pagination

• Rewrote component with flexbox.

• Explicit classes (.page-item, .page-link) are now required on the descendants of .paginations

• Dropped the .pager component entirely as it was little more than customized outline buttons.

Breadcrumbs

• An explicit class, .breadcrumb-item, is now required on the descendants of .breadcrumbs

Labels and badges

• Renamed .label to .badge to disambiguate from the <label> element.

• Dropped the .badge component as it was nearly identical to labels. Use the .badge-pill modifier together with the label component instead for that rounded look.

• Badges are no longer floated automatically in list groups and other components. Utility classes are now required for that.

• .badge-default has been dropped and .badge-secondary added to match component modifier classes used elsewhere.

Panels, thumbnails, and wells

Dropped entirely for the new card component.

Panels

• .panel to .card, now built with flexbox.

• .panel-default removed and no replacement.

• .panel-group removed and no replacement. .card-group is not a replacement, it is different.

• .panel-heading to .card-header

• .panel-title to .card-title. Depending on the desired look, you may also want to use heading elements or classes (e.g. <h3>, .h3) or bold elements or classes (e.g. <strong>, <b>, .font-weight-bold). Note that .card-title, while similarly named, produces a different look than .panel-title.

• .panel-body to .card-body

• .panel-footer to .card-footer

• .panel-primary, .panel-success, .panel-info, .panel-warning, and .panel-danger have been dropped for .bg-, .text-, and .border utilities generated from our $theme-colors Sass map.

Progress

• Replaced contextual .progress-bar-* classes with .bg-* utilities. For example, class="progress-bar progress-bar-danger" becomes class="progress-bar bg-danger".

Carousel

• Overhauled the entire component to simplify design and styling. We have fewer styles for you to override, new indicators, and new icons.

• All CSS has been un-nested and renamed, ensuring each class is prefixed with .carousel-.

• For carousel items, .next, .prev, .left, and .right are now .carousel-item-next, .carousel-item-prev, .carousel-item-left, and .carousel-item-right.

• .item is also now .carousel-item.

• For prev/next controls, .carousel-control.right and .carousel-control.left are now .carousel-control-next and .carousel-control-prev, meaning they no longer require a specific base class.

• Removed all responsive styling, deferring to utilities (e.g., showing captions on certain viewports) and custom styles as needed.

• Removed image overrides for images in carousel items, deferring to utilities.

• Tweaked the Carousel example to include the new markup and styles.

Tables

• Removed support for styled nested tables. All table styles are now inherited in v4 for simpler selectors.

• Added inverse table variant.

Utilities

• Display, hidden, and more:

• Made display utilities responsive (e.g., .d-none and d-{sm,md,lg,xl}-none).

• Dropped the bulk of .hidden-* utilities for new display utilities. For example, instead of .hidden-sm-up, use .d-sm-none. Renamed the .hidden-print utilities to use the display utility naming scheme. More info under the Responsive utilities section of this page.

• Added .float-{sm,md,lg,xl}-{left,right,none} classes for responsive floats and removed .pull-left and .pull-right since they’re redundant to .float-left and .float-right.

• Type:

• Added responsive variations to our text alignment classes .text-{sm,md,lg,xl}-{left,center,right}.

• Alignment and spacing:

• Added new responsive margin and padding utilities for all sides, plus vertical and horizontal shorthands.

• Added boatload of flexbox utilities.

• Dropped .center-block for the new .mx-auto class.

Vendor prefix mixins

Bootstrap 3’s vendor prefix mixins, which were deprecated in v3.2.0, have been removed in Bootstrap 4. Since we use Autoprefixer, they’re no longer necessary.

Removed the following mixins: animation, animation-delay, animation-direction, animation-duration, animation-fill-mode, animation-iteration-count, animation-name, animation-timing-function, backface-visibility, box-sizing, content-columns, hyphens, opacity, perspective, perspective-origin, rotate, rotateX, rotateY, scale, scaleX, scaleY, skew, transform-origin, transition-delay, transition-duration, transition-property, transition-timing-function, transition-transform, translate, translate3d, user-select

Documentation

Our documentation received an upgrade across the board as well. Here’s the low down:

• We’re still using Jekyll, but we have plugins in the mix:

• bugify.rb is used to efficiently list out the entries on our browser bugs page.

• example.rb is a custom fork of the default highlight.rb plugin, allowing for easier example-code handling.

• callout.rb is a similar custom fork of that, but designed for our special docs callouts.

• markdown-block.rb is used to to render Markdown snippets within HTML elements like tables.

• jekyll-toc is used to generate our table of contents.

• All docs content has been rewritten in Markdown (instead of HTML) for easier editing.

• Pages have been reorganized for simpler content and a more approachable hierarchy.

• We moved from regular CSS to SCSS to take full advantage of Bootstrap’s variables, mixins, and more.

Responsive utilities

All @screen- variables have been removed in v4.0.0. Use the media-breakpoint-up(), media-breakpoint-down(), or media-breakpoint-only() Sass mixins or the $grid-breakpoints Sass map instead.

Our responsive utility classes have largely been removed in favor of explicit display utilities.

• The .hidden and .show classes have been removed because they conflicted with jQuery’s $(...).hide() and $(...).show() methods. Instead, try toggling the [hidden] attribute or use inline styles like style="display: none;" and style="display: block;".

• All .hidden- classes have been removed, save for the print utilities which have been renamed.

• Removed from v3: .hidden-xs .hidden-sm .hidden-md .hidden-lg .visible-xs-block .visible-xs-inline .visible-xs-inline-block .visible-sm-block .visible-sm-inline .visible-sm-inline-block .visible-md-block .visible-md-inline .visible-md-inline-block .visible-lg-block .visible-lg-inline .visible-lg-inline-block

• Removed from v4 alphas: .hidden-xs-up .hidden-xs-down .hidden-sm-up .hidden-sm-down .hidden-md-up .hidden-md-down .hidden-lg-up .hidden-lg-down

• Print utilities no longer start with .hidden- or .visible-, but with .d-print-.

• Old names: .visible-print-block, .visible-print-inline, .visible-print-inline-block, .hidden-print

• New classes: .d-print-block, .d-print-inline, .d-print-inline-block, .d-print-none

Rather than using explicit .visible-* classes, you make an element visible by simply not hiding it at that screen size. You can combine one .d-*-none class with one .d-*-block class to show an element only on a given interval of screen sizes (e.g. .d-none.d-md-block.d-xl-none shows the element only on medium and large devices).

Note that the changes to the grid breakpoints in v4 means that you’ll need to go one breakpoint larger to achieve the same results. The new responsive utility classes don’t attempt to accommodate less common cases where an element’s visibility can’t be expressed as a single contiguous range of viewport sizes; you will instead need to use custom CSS in such cases.

 © 2011–2017 Twitter, Inc.

© 2011–2017 The Bootstrap Authors

Code licensed under the MIT License.

Documentation licensed under the Creative Commons Attribution License v3.0.