@import in @if statement in Sass

问题:

I want to load only the css needed for the login page for performance. On my other pages I want a grouped css file that will be cached on every page which contain all my css.

I have the following files:

minifiedcssforloginpage.scss
grouped-pages.scss

In minifiedcssforloginpage.scss I declare $load-complete-css:false. Afterwards I import myproject.scss which contains all the imports of my modules, layouts, core... In myproject.scss i want to do something like

@if $load-complete-css {
     @import module1;
     @import module2;
     @import module3;
}

So minifiedcssforloginpage.scss would generate minifiedcssforloginpage.css with less css then grouped-pages.css (that has a var $load-complete-css set to true).

But I get an error that this is not possible "Import directives may not be used within control directives or mixins".

回答1:

It's one of those things that's just not allowed. The only thing you can do is turn those imports into mixins (import the file outside the @if and call the mixin where appropriate).

Clarification:

_partial.scss

@mixin partial {
    .test { color: red }
    // other styles here
}

styles.scss

@import "partial";
@if $someval == true {
    @include partial;
}

回答2:

The core dev team is reluctant to implement this feature, although they are considering the implementation of a brand new dependency system.

---

See the following Github issues :

• Allow @import within @if (#451)
• Using @import statements within control directives or mixins (#779)
• Allow optional @imports (#779)
• Dynamic Dependencies (#739)

回答3:

Put your styles into various partial files in a way that makes sense to you. Then, you can have create a separate SASS file for your login page that imports only the files with the relevant styles.

To quote from my answer to another question:

It is currently not possible to use SASS to include files dynamically. @import cannot be used within control directives (e.g. @if) or mixins, using a variable in an import directive is erroneous syntax, and there is no directive for ending file execution early (which effectively would allow conditional imports). However, you can solve your issue by changing how you structure your style rules.

... If you have styles that [should be] conditionally included [they] should be encapsulated in mixins, in 'module' or 'library' files. ... The main idea is that importing one such file will not output any css. This way, you can import these files redundantly so you can use the mixins wherever you need them.