scss SASS:跨媒体查询占位符
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// ----
// Sass (v3.3.4)
// Compass (v1.0.0.alpha.18)
// ----
// -----------------------------------------------------------------------------
// Introduction
// -----------------------------------------------------------------------------
// Here is hacky and experimental solution for cross-scopes extends
// ---
// It works by generating one placeholder per breakpoint
// instead of a single placeholder at root level as you'd normally do
// (in a fully automatic way of course)
// ---
// The API is quite simple.
// To create a placeholder, instead of doing:
// %my-awesome-placeholder {}
// You would do:
// @include placeholder(my-awesome-placeholder)
// ---
// To extend an existing placeholder, instead of doing:
// @extend %my-awesome-placeholder
// You would do:
// @include _(my-awesome-placeholder)
// ---
// -----------------------------------------------------------------------------
// Set up
// -----------------------------------------------------------------------------
// A list of breakpoints
// When generating a placeholder,
// The same placeholder will be generated in every breakpoint
$breakpoints: (
"small" : 600px,
"medium" : 900px,
"large" : 1200px
);
// -----------------------------------------------------------------------------
// Core
// -----------------------------------------------------------------------------
// Caching current breakpoint
// Not meant to be manually edited
$default-breakpoint: root;
$current-breakpoint: $default-breakpoint;
// Caching existing placeholders
// Not meant to be manually edited
$placeholders: ();
// The usual breakpoint mixin
// Except it updates the $current-breakpoint variable
// 1. If breakpoint name exists in map
// 2. Update $current-breakpoint
// 3. Open a media query
// 4. Let the user dump content
// 5. Then reset $current-breakpoint
// 6. If breakpoint name doesn't exist in map, warn the user
@mixin breakpoint($breakpoint) {
$value: map-get($breakpoints, $breakpoint);
@if $value != null { // 1
$current-breakpoint: $breakpoint !global; // 2
@media (min-width: $value) { @content; } // 3
$current-breakpoint: $default-breakpoint !global; // 5
}
@else {
@warn "Invalid breakpoint `#{$breakpoint}`."; // 6
}
}
// Generating placeholders
// actually generating one placeholder per breakpoint
// 1. If placeholder doesn't exist yet
// 2. Store the name
// 3. Looping through all the breakpoints
// 4. Opening a media query
// 5. Generating a placeholder at root level
// 6. With desired content
// 7. And dumping a placeholder out of any media query
// 8. If placeholder already exist, warn the user
@mixin placeholder($name) {
@if not index($placeholders, $name) { // 1
$placeholders: append($placeholders, $name) !global; // 2
@at-root {
@each $breakpoint, $value in $breakpoints { // 3
@media (min-width: $value) { // 4
%#{$name}-#{$breakpoint} { // 5
@content; // 6
}
}
}
%#{$name}-#{$default-breakpoint} { // 7
@content;
}
}
}
@else {
@warn "Placeholder `#{$name}` already exists."; // 8
}
}
// Extend the accurate placeholder
// according to the current scope
// Basically instead of doing:
// @extend %clear;
// You go:
// @include _(clear);
// Not much longer, is it?
@mixin _($name) {
@extend %#{$name}-#{$current-breakpoint} !optional;
}
// -----------------------------------------------------------------------------
// Generating a placeholder
// -----------------------------------------------------------------------------
// Creating placeholders
// A simple one in our case
// But it could have much more content
// ---
// Basically instead of doing:
// %clear { ... }
// You go:
// @include placeholder('clear') { ... }
@include placeholder('clear') {
clear: both;
}
// -----------------------------------------------------------------------------
// Extending a placeholder
// -----------------------------------------------------------------------------
// At root level
.a {
@include _(clear); // Same as @extend %clear
}
.b {
@include _(clear);
}
// In a nested media query
.c {
@include breakpoint(medium) {
@include _(clear);
}
}
// In an outer media query
@include breakpoint(medium) {
.d {
@include _(clear);
}
}
// Both in a nested media query and at root level
.e {
@include _(clear);
@include breakpoint(large) {
@include _(clear);
}
}
// Have a look at the CSS output on the right.
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