数字

Sass 中的数字有两个组成部分：数字本身及其单位。例如，在 16px 中，编号为 16，单位为 px。数字可以没有单位，也可以有复数单位。详情请参阅下面的 单位。

Playground

SCSS Syntax

@debug 100; // 100
@debug 0.8; // 0.8
@debug 16px; // 16px
@debug 5px * 2px; // 10px*px (read "square pixels")
Playground

Sass Syntax

@debug 100  // 100
@debug 0.8  // 0.8
@debug 16px  // 16px
@debug 5px * 2px  // 10px*px (read "square pixels")

Sass 数字支持与 CSS 数字相同的格式，包括 科学计数法，它是在数字及其 10 的幂之间用 e 编写的。由于浏览器对科学记数法的支持历来不稳定，因此 Sass 总是将其编译为完全扩展的数字。

¥Sass numbers support the same formats as CSS numbers, including scientific notation, which is written with an e between the number and its power of 10. Because support for scientific notation in browsers has historically been spotty, Sass always compiles it to fully expanded numbers.

Playground

SCSS Syntax

@debug 5.2e3; // 5200
@debug 6e-2; // 0.06
Playground

Sass Syntax

@debug 5.2e3  // 5200
@debug 6e-2  // 0.06

⚠️ Heads up!

Sass 不区分整数和小数，因此例如 math.div(5, 2) 返回 2.5 而不是 2。这与 JavaScript 的行为相同，但与许多其他编程语言不同。

¥Sass doesn’t distinguish between whole numbers and decimals, so for example math.div(5, 2) returns 2.5 rather than 2. This is the same behavior as JavaScript, but different than many other programming languages.

UnitsUnits permalink

Sass has powerful support for manipulating units based on how real-world unit calculations work. When two numbers are multiplied, their units are multiplied as well. When one number is divided by another, the result takes its numerator units from the first number and its denominator units from the second. A number can have any number of units in the numerator and/or denominator.

Playground

SCSS Syntax

@use 'sass:math';

@debug 4px * 6px; // 24px*px (read "square pixels")
@debug math.div(5px, 2s); // 2.5px/s (read "pixels per second")

// 3.125px*deg/s*em (read "pixel-degrees per second-em")
@debug 5px * math.div(math.div(30deg, 2s), 24em);

$degrees-per-second: math.div(20deg, 1s);
@debug $degrees-per-second; // 20deg/s
@debug math.div(1, $degrees-per-second); // 0.05s/deg
Playground

Sass Syntax

@use 'sass:math'

@debug 4px * 6px  // 24px*px (read "square pixels")
@debug math.div(5px, 2s)  // 2.5px/s (read "pixels per second")

// 3.125px*deg/s*em (read "pixel-degrees per second-em")
@debug 5px * math.div(math.div(30deg, 2s), 24em)

$degrees-per-second: math.div(20deg, 1s)
@debug $degrees-per-second  // 20deg/s
@debug math.div(1, $degrees-per-second)  // 0.05s/deg

⚠️ Heads up!

Because CSS doesn’t support complex units like square pixels, using a number with complex units as a property value will produce an error. This is a feature in disguise, though; if you aren’t ending up with the right unit, it usually means that something’s wrong with your calculations! And remember, you can always use the @debug rule to check out the units of any variable or expression.

Sass will automatically convert between compatible units, although which unit it will choose for the result depends on which implementation of Sass you’re using. If you try to combine incompatible units, like 1in + 1em, Sass will throw an error.

Playground

SCSS Syntax

// CSS defines one inch as 96 pixels.
@debug 1in + 6px; // 102px or 1.0625in

@debug 1in + 1s;
//     ^^^^^^^^
// Error: Incompatible units s and in.
Playground

Sass Syntax

// CSS defines one inch as 96 pixels.
@debug 1in + 6px  // 102px or 1.0625in

@debug 1in + 1s
//     ^^^^^^^^
// Error: Incompatible units s and in.

As in real-world unit calculations, if the numerator contains units that are compatible with units in the denominator (like math.div(96px, 1in)), they’ll cancel out. This makes it easy to define a ratio that you can use for converting between units. In the example below, we set the desired speed to one second per 50 pixels, and then multiply that by the number of pixels the transition covers to get the time it should take.

Playground

SCSS Syntax

@use 'sass:math';

$transition-speed: math.div(1s, 50px);

@mixin move($left-start, $left-stop) {
  position: absolute;
  left: $left-start;
  transition: left ($left-stop - $left-start) * $transition-speed;

  &:hover {
    left: $left-stop;
  }
}

.slider {
  @include move(10px, 120px);
}
Playground

Sass Syntax

@use 'sass:math'

$transition-speed: math.div(1s, 50px)

@mixin move($left-start, $left-stop)
  position: absolute
  left: $left-start
  transition: left ($left-stop - $left-start) * $transition-speed

  &:hover
    left: $left-stop



.slider
  @include move(10px, 120px)

CSS Output

.slider {
  position: absolute;
  left: 10px;
  transition: left 2.2s;
}
.slider:hover {
  left: 120px;
}

⚠️ Heads up!

If your arithmetic gives you the wrong unit, you probably need to check your math. You may be leaving off units for a quantity that should have them! Staying unit-clean allows Sass to give you helpful errors when something isn’t right.

You should especially avoid using interpolation like #{$number}px. This doesn’t actually create a number! It creates an unquoted string that looks like a number, but won’t work with any number operations or functions. Try to make your math unit-clean so that $number already has the unit px, or write $number * 1px.

⚠️ Heads up!

Percentages in Sass work just like every other unit. They are not interchangeable with decimals, because in CSS decimals and percentages mean different things. For example, 50% is a number with % as its unit, and Sass considers it different than the number 0.5.

You can convert between decimals and percentages using unit arithmetic. math.div($percentage, 100%) will return the corresponding decimal, and $decimal * 100% will return the corresponding percentage. You can also use the math.percentage() function as a more explicit way of writing $decimal * 100%.

精确精确 permalink

¥Precision

兼容性 (10 Digit Default):
Dart Sass
✓
LibSass
✗
Ruby Sass
since 3.5.0

LibSass 和旧版本的 Ruby Sass 默认采用 5 位数字精度，但可以配置为使用不同的数字。建议用户将它们配置为 10 位数字，以获得更高的准确性和前向兼容性。

¥LibSass and older versions of Ruby Sass default to 5 digits of numeric precision, but can be configured to use a different number. It’s recommended that users configure them for 10 digits for greater accuracy and forwards-compatibility.

Sass 数字在内部表示为 64 位浮点值。当序列化为 CSS 并出于平等目的时，它们支持小数点后最多 10 位精度。这意味着一些不同的事情：

¥Sass numbers are represented internally as 64-bit floating point values. They support up to 10 digits of precision after the decimal point when serialized to CSS and for the purposes of equality. This means a few different things:

  • 生成的 CSS 中仅包含小数点后的前十位数字。

    ¥Only the first ten digits of a number after the decimal point will be included in the generated CSS.

  • 如果两个数字小数点后第十位相同，则像 == 和 >= 这样的运算将认为两个数字相等。

    ¥Operations like == and >= will consider two numbers equivalent if they’re the same up to the tenth digit after the decimal point.

  • 如果一个数字与整数的距离小于 0.0000000001，则对于需要整数参数的函数（如 list.nth()）而言，它被视为整数。

    ¥If a number is less than 0.0000000001 away from an integer, it’s considered to be an integer for the purposes of functions like list.nth() that require integer arguments.

Playground

SCSS Syntax

@debug 0.012345678912345; // 0.0123456789
@debug 0.01234567891 == 0.01234567899; // true
@debug 1.00000000009; // 1
@debug 0.99999999991; // 1
Playground

Sass Syntax

@debug 0.012345678912345  // 0.0123456789
@debug 0.01234567891 == 0.01234567899  // true
@debug 1.00000000009  // 1
@debug 0.99999999991  // 1

💡 Fun fact:

当数字用在与精度相关的地方时，它们会懒惰地四舍五入到 10 位精度。这意味着数学函数将在内部使用完整数值，以避免累积额外的舍入误差。

¥Numbers are rounded to 10 digits of precision lazily when they’re used in a place where precision is relevant. This means that math functions will work with the full number value internally to avoid accumulating extra rounding errors.