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概要
本文以一个按钮开发的实例，介绍如何使用SASS来简化CSS代码开发的。
代码和实现
我们希望通过CSS开发下面的代码样式，从样式来看，每个按钮的基本样式相同，就是颜色不同。
如果按照传统的方式开发，需要开发btn ，btn-primary，btn-danger和btn-succsess四个类，比较麻烦，所以先将公共样式提取出来，放到btn类中。
在btn类中，封装所有公共样式，代码如下：
btn{font-size: 1rem;font-weight: 400;padding:.375rem .75rem;line-height: 1.5;text-align: center;vertical-align:middle;text-decoration: none;user-select: none;border-radius: .375rem;cursor: pointer;transition: color .15s ease-in-out, background-color .15s ease-in-out, border-color .15s ease-in-out, box-shadow .15s ease-in-out;
}
每个按钮主要区别是颜色不同，每个按钮的颜色在active，disabled和hover时候，也会有一些差异，如果一个类一个类的写，显然比较麻烦。因此先将这些颜色通过SASS的变量定义出来：
$buttons:("type":"primary", "bgColor": #0d6efd, "fontColor": #fff, "borderColor":#0d6efd),
("type":"success", "bgColor": #198754, "fontColor": #fff, "borderColor":#198754),
("type":"danger", "bgColor": #dc3545, "fontColor": #fff, "borderColor":#dc3545),
("type":"warning", "bgColor": #ffc107, "fontColor": #fff, "borderColor":#ffc720),
("type":"info", "bgColor": #0dcaf0, "fontColor": #000,"borderColor": #25cff2);
通过循环遍历，一次生成所有需要的类。
对于按钮在hover，disabled和active状态下，颜色略有区别的需求，我们可以先设置一个基准颜色，再使用SASS的颜色函数lighten和darken将基准颜色变深或变浅。
@each $btn in $buttons {.btn-#{map.get($btn,"type")}{@extend .btn;background-color: map.get($btn,"bgColor");border:1px solid map.get($btn,"borderColor");color: map.get($btn,"fontColor");;&:hover {background-color: lighten(map.get($btn,"bgColor"), 10%);border:1px solid lighten(map.get($btn,"borderColor"), 10%);color: map.get($btn,"fontColor");}&:disabled{background-color: lighten(map.get($btn,"bgColor"), 20%);border:1px solid lighten(map.get($btn,"borderColor"), 20%);color: map.get($btn,"fontColor");}&:active {background-color: darken(map.get($btn,"bgColor"), 10%);border:1px solid darken(map.get($btn,"borderColor"), 10%);;color: map.get($btn,"fontColor");}}
}
对于生成CSS类，以btn-primary为例，它和btn类的关系应该是继承关系，因此使用@extend，编译后生成的CSS代码如下：
.btn, .btn-primary {font-size: 1rem;font-weight: 400;padding: 0.375rem 0.75rem;line-height: 1.5;text-align: center;vertical-align: middle;text-decoration: none;-webkit-user-select: none;-moz-user-select: none;user-select: none;border-radius: 0.375rem;cursor: pointer;transition: color 0.15s ease-in-out, background-color 0.15s ease-in-out, border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out;
}.btn-primary {background-color: #0d6efd;border: 1px solid #0d6efd;color: #fff;
}
此处推荐使用@extend，如果使用@mixin，生成的CSS代码并不合理。
如果使用@mixin，生成的CSS代码如下：
.btn-primary {font-size: 1rem;font-weight: 400;padding: 0.375rem 0.75rem;line-height: 1.5;text-align: center;vertical-align: middle;text-decoration: none;-webkit-user-select: none;-moz-user-select: none;user-select: none;border-radius: 0.375rem;cursor: pointer;transition: color 0.15s ease-in-out, background-color 0.15s ease-in-out, border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out;background-color: #0d6efd;border: 1px solid #0d6efd;color: #fff;
}
.btn-primary:hover {background-color: #408cfd;border: 1px solid #408cfd;color: #fff;
}
.btn-primary:disabled {background-color: #72abfe;border: 1px solid #72abfe;color: #fff;
}
.btn-primary:active {background-color: #0257d5;border: 1px solid #0257d5;color: #fff;
}可以看到公共样式被定义到了每个具体的类中，造成了大量冗余的代码。
附录
html代码：
<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Buttons</title><link rel="stylesheet" href="style.css">
</head>
<body><div class="buttons"><button class="btn btn-primary">Primary</button><button class="btn btn-success">Success</button><button class="btn btn-danger">Danger</button><button class="btn btn-warning">Warning</button><button class="btn btn-info">Info</button> </div>
</body>
</html>
SASS代码：
@use "sass:map";
* {padding: 0;margin: 0;box-sizing: border-box;
}.btn{font-size: 1rem;font-weight: 400;padding:.375rem .75rem;line-height: 1.5;text-align: center;vertical-align:middle;text-decoration: none;user-select: none;border-radius: .375rem;cursor: pointer;transition: color .15s ease-in-out, background-color .15s ease-in-out, border-color .15s ease-in-out, box-shadow .15s ease-in-out;
}$buttons:("type":"primary", "bgColor": #0d6efd, "fontColor": #fff, "borderColor":#0d6efd),
("type":"success", "bgColor": #198754, "fontColor": #fff, "borderColor":#198754),
("type":"danger", "bgColor": #dc3545, "fontColor": #fff, "borderColor":#dc3545),
("type":"warning", "bgColor": #ffc107, "fontColor": #fff, "borderColor":#ffc720),
("type":"info", "bgColor": #0dcaf0, "fontColor": #000,"borderColor": #25cff2);
@each $btn in $buttons {.btn-#{map.get($btn,"type")}{@extend .btn;background-color: map.get($btn,"bgColor");border:1px solid map.get($btn,"borderColor");color: map.get($btn,"fontColor");;&:hover {background-color: lighten(map.get($btn,"bgColor"), 10%);border:1px solid lighten(map.get($btn,"borderColor"), 10%);color: map.get($btn,"fontColor");}&:disabled{background-color: lighten(map.get($btn,"bgColor"), 20%);border:1px solid lighten(map.get($btn,"borderColor"), 20%);color: map.get($btn,"fontColor");}&:active {background-color: darken(map.get($btn,"bgColor"), 10%);border:1px solid darken(map.get($btn,"borderColor"), 10%);;color: map.get($btn,"fontColor");}}
}