null

该值null是其类型的唯一值。它表示缺少值，通常由函数返回以表示缺少结果。

SCSS
Sass
SCSS  语法@use "sass:map";
@use "sass:string";

@debug string.index("Helvetica Neue", "Roboto"); // null
@debug map.get(("large": 20px), "small"); // null
@debug &; // null
Sass语法@use "sass:map"
@use "sass:string"

@debug string.index("Helvetica Neue", "Roboto")  // null
@debug map.get(("large": 20px), "small")  // null
@debug &  // null

如果列表包含null，null则会在生成的CSS中将其省略。

SCSS
Sass
css
SCSS  语法$fonts: ("serif": "Helvetica Neue", "monospace": "Consolas");

h3 {
  font: 18px bold map-get($fonts, "sans");
}
Sass语法$fonts: ("serif": "Helvetica Neue", "monospace": "Consolas")

h3
  font: 18px bold map-get($fonts, "sans")

CSS  输出h3 {
  font: 18px bold;
}

如果属性值为null，则将完全省略该属性。

SCSS
Sass
css
SCSS  语法$fonts: ("serif": "Helvetica Neue", "monospace": "Consolas");

h3 {
  font: {
    size: 18px;
    weight: bold;
    family: map-get($fonts, "sans");
  }
}
Sass语法$fonts: ("serif": "Helvetica Neue", "monospace": "Consolas")

h3
  font:
    size: 18px
    weight: bold
    family: map-get($fonts, "sans")


CSS  输出h3 {
  font-size: 18px;
  font-weight: bold;
}

null也是falsey，这意味着它对false所有采用布尔值的规则或运算符都算在内。这使得它易于使用的值，可以是null作为条件@if和if()。

SCSS
Sass
css
SCSS  语法@mixin app-background($color) {
  #{if(&, '&.app-background', '.app-background')} {
    background-color: $color;
    color: rgba(#fff, 0.75);
  }
}

@include app-background(#036);

.sidebar {
  @include app-background(#c6538c);
}
Sass语法@mixin app-background($color)
  #{if(&, '&.app-background', '.app-background')}
    background-color: $color
    color: rgba(#fff, 0.75)



@include app-background(#036)

.sidebar
  @include app-background(#c6538c)

CSS  输出.app-background {
  background-color: #036;
  color: rgba(255, 255, 255, 0.75);
}

.sidebar.app-background {
  background-color: #c6538c;
  color: rgba(255, 255, 255, 0.75);
}