null

值 null 是其类型的唯一值。它表示值的缺失，通常由函数返回以指示没有结果。

Playground

SCSS Syntax

@use "sass:map";
@use "sass:string";

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

Sass Syntax

@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，则该 null 将从生成的 CSS 中省略。

Playground

SCSS Syntax

$fonts: ("serif": "Helvetica Neue", "monospace": "Consolas");

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

Sass Syntax

$fonts: ("serif": "Helvetica Neue", "monospace": "Consolas")

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

CSS Output

h3 {
  font: 18px bold;
}

如果属性值是 null，则完全省略该属性。

Playground

SCSS Syntax

$fonts: ("serif": "Helvetica Neue", "monospace": "Consolas");

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

Sass Syntax

$fonts: ("serif": "Helvetica Neue", "monospace": "Consolas")

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

CSS Output

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

null 也是假值，这意味着对于任何需要布尔值的规则或运算符，它都被视为 false。这使得使用可能为 null 的值作为 @if 和 if() 的条件变得很容易。

Playground

SCSS Syntax

@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);
}
Playground

Sass Syntax

@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 Output

.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);
}