借助sass的Maps功能使得响应式代码更有条理_html/css

借助sass的Maps功能使得响应式代码更有条理_html/css_WEB-ITnose

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Release： 2016-06-24 11:35:43

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原文来自这里
本文综合了原文(by Jonathan Suh)以及笔者自己的理解。

Introduction

众所周知，写代码与写维护性高的代码是两回事.而涉及到响应式,代码又特别容易变的杂乱.借助sass maps所提供的拓扑功能,我们可以尝试减轻这一痛点.
以下的代码还是很常见的:

p { font-size: 15px; }@media screen and (min-width: 480px) {  p { font-size: 16px; }}@media screen and (min-width: 640px) {  p { font-size: 17px; }}@media screen and (min-width: 1024px) {  p { font-size: 19px; }}

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两个问题点：1.DRY, 2.Magic Number.
也许sass的变量可以解决问题2。

$p-font-size-mobile : 15px;$p-font-size-small  : 16px;$p-font-size-medium : 17px;$p-font-size-large  : 19px;

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但是变量多了之后，代码会变成这样：

$p-font-size-mobile : 15px;$p-font-size-small  : 16px;$p-font-size-medium : 17px;$p-font-size-large  : 19px;$h1-font-size-mobile: 28px;$h1-font-size-small : 31px;$h1-font-size-medium: 33px;$h1-font-size-large : 36px;..............

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超多的变量显得毫无章法。

Sass maps初试

声明如下的sass变量:

$p-font-sizes: (  null  : 15px,  480px : 16px,  640px : 17px,  1024px: 19px);

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接下来,创建mixin,遍历属性,生成对应的media queries

@mixin font-size($fs-map) {  @each $fs-breakpoint, $fs-font-size in $fs-map {    @if $fs-breakpoint == null {      font-size: $fs-font-size;    }    @else {      @media screen and (min-width: $fs-breakpoint) {        font-size: $fs-font-size;      }    }  }}

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Sass 还提供了一些其它的语法糖,可以参考这里

这时我们可以在任意的地方引入mixin

p {  @include font-size($p-font-sizes);}

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结果和文章开头是一样的.

Solving Breakpoint Fragmentation

上面的代码似乎还是有一点脆弱,如果我们希望引入更多的Breakpoint,或着说p tag 与h1 tag 希望引入不同的Breakpoint.事情就会变的很麻烦.考虑到这一点,我们可以将代码进行重构.

$breakpoints: (  small : 480px,  medium: 700px, // Previously 640px  large : 1024px);$p-font-sizes: (  null  : 15px,  small : 16px,  medium: 17px,  large : 19px);$h1-font-sizes: (  null  : 28px,  small : 31px,  medium: 33px,  large : 36px);@mixin font-size($fs-map, $fs-breakpoints: $breakpoints) {  @each $fs-breakpoint, $fs-font-size in $fs-map {    @if $fs-breakpoint == null {      font-size: $fs-font-size;    }    @else {      // If $fs-font-size is a key that exists in      // $fs-breakpoints, use the value      @if map-has-key($fs-breakpoints, $fs-breakpoint) {        $fs-breakpoint: map-get($fs-breakpoints, $fs-breakpoint);      }      @media screen and (min-width: $fs-breakpoint) {        font-size: $fs-font-size;      }    }  }}

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现在,我们可以随意的添加Breakpoint

$p-font-sizes: (  null  : 15px,  small : 16px,  medium: 17px,  900px : 18px,  large : 19px,  1440px: 20px,);p {  @include font-size($p-font-sizes);}

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Improving Vertical Rhythm With Line Height

来,更进一步,我们可以font-size mixin中增加一个lineheight的配置,(line-height和font-size常常是同时出现的)

$breakpoints: (  small : 480px,  medium: 700px,  large : 1024px);$p-font-sizes: (  null  : (15px, 1.3),  small : 16px,  medium: (17px, 1.4),  900px : 18px,  large : (19px, 1.45),  1440px: 20px,);@mixin font-size($fs-map, $fs-breakpoints: $breakpoints) {  @each $fs-breakpoint, $fs-font-size in $fs-map {    @if $fs-breakpoint == null {      @include make-font-size($fs-font-size);    }    @else {      // If $fs-font-size is a key that exists in      // $fs-breakpoints, use the value      @if map-has-key($fs-breakpoints, $fs-breakpoint) {        $fs-breakpoint: map-get($fs-breakpoints, $fs-breakpoint);      }      @media screen and (min-width: $fs-breakpoint) {        @include make-font-size($fs-font-size);      }    }  }}// Utility function for mixin font-size@mixin make-font-size($fs-font-size) {  // If $fs-font-size is a list, include  // both font-size and line-height  @if type-of($fs-font-size) == "list" {    font-size: nth($fs-font-size, 1);    @if (length($fs-font-size) > 1) {      line-height: nth($fs-font-size, 2);    }  }  @else {    font-size: $fs-font-size;  }}

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nth 是sass提供的语法,nth(list, n)从list中拿第n个数据.