Sass/Less 比較

變數

Sass             | Less
-----------------+-----------------
$color: red;     | @color: red;
div {            | div {
  color: $color; |   color: @color;
}                | }

兩種語言都支持選擇器內的範圍變數。但兩者行為上稍微有些不同：

Sass                     | Less
-------------------------+-----------------
$color: black;           | @color: black;
.scoped {                | .scoped {
  $bg: blue;             |   @bg: blue;
  $color: white;         |   @color: white;
  color: $color;         |   color: @color;
  background-color: $bg; |   background-color: @bg;
}                        | }
.unscoped {              | .unscoped {
  color: $color;         |   color: @color;
  // Would be an error   |   // Would be an error
  // background: $bg;    |   // background: @bg;
}                        | }

輸出：

Sass Output                 | Less Output
----------------------------+----------------------------
.scoped {                   | .scoped {
  color: white;             |   color: white;
  background-color: blue;   |   background-color: blue;
}                           | }
.unscoped { color: white; } | .unscoped { color: black; }

巢狀選擇

Sass跟Less都有&選擇子允許存取父節點。

Sass               | Less
-------------------+-----------------
p {                | p {
  a {              |   a {
    color: red;    |     color: red;
    &:hover {      |     &:hover {
      color: blue; |       color: blue;
    }              |     }
  }                |   }
}                  | }

Mixins(混合)

Sass                              | Less
----------------------------------+----------------------------------
@mixin bordered {                 | .bordered {
  border-top: dotted 1px black;   |   border-top: dotted 1px black;
  border-bottom: solid 2px black; |   border-bottom: solid 2px black;
}                                 | }
                                  | 
#menu a {                         | #menu a {
  @include bordered;              |   .bordered;
}                                 | }

有變數的混合 / 動態混合

Sass                              | Less
----------------------------------+----------------------------------
@mixin bordered($width: 2px) {    | .bordered(@width: 2px) {
  border: $width solid black;     |   border: @width solid black;
}                                 | }
                                  | 
#menu a {                         | #menu a {
  @include bordered(4px);         |   .bordered(4px);
}                                 | }

選擇器繼承

Less不支援繼承

Sass                        | Less  | CSS Output
----------------------------+-------+---------------------------
.bordered {                 |  N/A  | .bordered, #menu a {
  border: 1px solid back;   |       |   border: 1px solid back; }
}                           |       |
                            |       |
#menu a {                   |       |
  @extend .bordered;        |       |
}                           |       |

顏色

Less跟Sass都提供顏色數學運算。我不知道為什麼Less會實作這個東西，因為他在Sass是個爛主意。

Sass提供一系列處理顏色的工具，所有的顏色表達式都視為與顏色相同並可以被處理。

Sass exposes a long list of color functions not found in CSS:

Accessors:

red($color)
green($color)
blue($color)
hue($color)
saturation($color)
lightness($color)
alpha($color)

Mutators:

lighten($color, $amount)
darken($color, $amount)
saturate($color, $amount)
desaturate($color, $amount)
adjust-hue($color, $amount)
opacify($color, $amount)
transparentize($color, $amount)
mix($color1, $color2[, $amount])
grayscale($color)
compliment($color)

Note: Less.js provides a number of similar color functions.

Numbers

Both Sass and Less support numbers and basic arithmetic. However they differ significantly with respect to how they handle units.

Sass supports unit-based arithmetic, just like you learned in school. Complex units are supported in any intermediate form and will only raise an error if you try to print out the value of a complex unit.

Additionally, Sass has conversion tables so that any comparable units can be combined.

Sass will let you define your own units and will happily print out unknown units into your css. Less will not. Sass does this as a form of future proofing against changes in the w3c specification or in case a browser introduces a non-standard unit.

Sass:

1cm * 1em => 1 cm * em
2in * 3in => 6 in * in
(1cm / 1em) * 4em => 4cm
2in + 3cm + 2pc => 3.514in
3in / 2in => 1.5

Less:

1cm * 1em => Error
2in * 3in => 6in
(1cm / 1em) * 4em => Error
2in + 3cm + 2pc => Error
3in / 2in => 1.5in

Conditionals & Control Structures

Less does not provide any conditionals or looping structures. Instead, it provides mixin guards and pattern-matching which can be used to similar effect.

Sass and Less provides provide boolean types true and false, the and, or, and not operators as well as <, >, <=, >=, == operators. There are minor syntax differences between the two (Sass syntax shown here).

Some sass examples:

@if lightness($color) > 30% {
  background-color: black;
}
@else {
  background-color: white;
}

Looping:

@for $i from 1px to 10px {
  .border-#{i} {
    border: $i solid blue;
  }
}

A similar example in Less, using mixins:

.mixin (@color) when (lightness(@color) > 30%) {
  background-color: black;
}
.mixin (@color) when (lightness(@color) =< 30%) {
  background-color: white;
}

Less supports looping via recursion, but not (yet) selector interpolation as shown in the Sass example, so it is of limited use.

Server Side Imports

Both sass and less will import other sass and less files.

Output formatting

Less has three output formats: normal, compressed & yui-compressed. Sass has four: nested, compact, compressed, expanded.

Sass output compression currently beats the google pagespeed css plugin output by a few percent.

Comments

Less and Sass both support C-style (/* */) and C++ Style comments (//).

Namespaces

Less provides a feature that Sass does not:

#bundle () {
  .red { background-color: red }
  .green { background-color: green }
}

.foo {
  #bundle > .red;
}

Generates:

.foo {
  background-color: red;
}

The sass team considered this feature and decided that adding it would create fragility and unexpected interconnectedness.

alivedise/sass_and_less_compared.markdown