Check if SASS parent selector exists. Is it possible

问题

I have a question. So in a mixing I am making a reference to the parent selector "&". This works as long as the mixin is not nested. Is there a way to to detect if the mixing is being used in a non nested scenario, or to check if "&" is null?

This works when the mixin call is not nested

=myresponsiveMixin($media)
  @if $media == small {
    @media only screen and (max-width: $break-small)
       @content
  @else if $media == medium
    @media only screen and (min-width: $break-small + 1) and (max-width: $break-large - 1)
       @content

This works great when the mixin call is nested, but will not resolve '&' when not nested

 =myresponsiveMixin($media)
      @if $media == small {
        @media only screen and (max-width: $break-small)
           .classInHTMLToAllowMediaQueries &
               @content
      @else if $media == medium
        @media only screen and (min-width: $break-small + 1) and (max-width: $break-large - 1)
           .classInHTMLToAllowMediaQueries &
               @content

So the question is, if there is a way to be able to check the value of parent selector "&", so I can cover all bases in a single mixin?

回答1:

@mixin does-parent-exist {
  @if & {
    .exists & {
      color: red;
    }
  } @else {
    .doesnt-exist {
      color: red;
    }
  }
}

http://sass-lang.com/documentation/file.SASS_REFERENCE.html#parent-script

回答2:

You're trying a wrong solution to solve your issue.

Have a look at how this problem is addressed in powerful SASS frameworks. Let's take Susy by Eric Meyer as a great example.

Let's imagine you've got the following HTML:

<div class="container">
  <div class="parent">
    <div class="child">
      Bla bla
    </div>
  </div>
</div>

When you call a mixin for the first time, you're doing it simply (the code is in the indented .sass syntax):

$total-columns: 8 // Declaring a varible that will be used by the mixin

.parent
  +span-columns(4) // Span four of eight columns

But when you call that for a child element, the proportions would be crooked, because the parent is already proportioned:

.child
  +span-columns(2) // This will fail. You want 2 of 8 columns,
                   // but due to nesting the math is crooked.
                   // It will be "2 of (4 of 8)".

To address the issue, you provide an optional argument: a context that is used to do the math:

.child
  +span-columns(2, 4) // Now the mixin will take 2 parts of 4
                      // instead of 2 parts of four

The source code for this mixin is available on GitHub.

In short, it creates an optional argument like this (the code is in the CSS-like .scss syntax):

@mixin span-columns(
  $columns,
  $context: $total-columns
  //...
) {
  //...
  width: columns($cols, $context /*...*/);
  //...
}

See how $context has a default value? Thanks to the default value this argument can be omitted. In other words, $context is an optional argument.

When calling this mixin, if $context is not provided (e. g. span-columns(2)), then it is set equal to $total-columns. The $total-columns variable should be set prior to calling the mixin for the first time (see my example above).

Then the two arguments are used to calculate the width.

UPD 2013-03-30

I am not trying to figure out things in regards to columns... I have modifier my question to make it clearer.

First of all, my recommendation concerns not only grid columns. It's a universal technique you can adopt.

Secondly, now i see that you're trying to nest media queries.

Well, some media queries of different type can be combined in CSS3: e. g. print and width. But you can't put a min-width: 601px inside max-width: 600px, this just won't work!

There's an extensive answer here on StackOverflow describing why you should not nest media queries of the same type: https://stackoverflow.com/a/11747166/901944

Thirdly, you're trying to invent the wheel. There's already a fantastic mixin for crunching media queries: Respond To by Snugug. It's super easy to use and very effective.

Fourthly, the XY thing. Instead of asking about your crooked mixin, please describe the problem that you're trying to solve with it! Show us the actual HTML and explain what behavior you would like to achieve.

We will show you that it can be solved with a simple, elegant, semantic solution that does not require SASS hacking.

来源：https://stackoverflow.com/questions/15668539/check-if-sass-parent-selector-exists-is-it-possible

标签

Sass