Can I update SASS variables in Media Queries?

问题:

Consider the following SASS code. I want to make sure that if the screen is above 1250px then the margin-top should be 750px and then it should change depending on size. However SASS does not allow me to update the variables inside the strings.

// Above 1250px
$pageTemplateMargin:750px;

// Below 1250px
@media screen and (max-width:1250px){
    $pageTemplateMargin:550px;
}

// Below 950px
@media screen and (max-width:950px){
    $pageTemplateMargin:450px;
}

@media screen and (max-width:850px){
    $pageTemplateMargin:150px;
}

@media screen and (max-width:750px){
    $pageTemplateMargin:250px;
}

// Render the correct code
.page-template {margin-top:$pageTemplateMargin}

Is there a better way for this, as it does not work and page-template stays at 750px.

Thanks

回答1:

I agree with the accepted answer that it's better to use maps in this case but I want to point out a couple of things.

Variables can actually be updated inside of media queries. The problem is that a variable defined outside of a block is a global variable while one defined within a block is a local variable. You can let sass treat a variable within a block as a global variable using the !global keyword.

$pageTemplateMargin:750px;

@media screen and (max-width:1250px){
    $pageTemplateMargin: 550px !global;
}

.page-template {
  margin-top: $pageTemplateMargin //will use 550px instead of 750px
}

Just want to clarify that it is possible albeit it is not appropriate in this use case.

I also suggest using a loop for your code which will prove helpful especially if you add more screen widths and margin properties so you don't need to further write more media queries.

$breakpoints: (
  1200px: 10px,
  1000px: 15px,
  800px: 20px,
);

@each $width, $margin in $breakpoints {
  @media screen and (max-width: $width) {
    .element {
      margin-top: $margin;
    }
  }
}

Hope this helps.

回答2:

No, you can't (in this situation, as pointed out in the other answer).

I'd suggest using mixins to work with this:

@mixin pageTemplateMargin($px) {
    margin-top: $px
}

@media screen and (max-width:1250px) {
    .element { @include pageTemplateMargin(10px);}
}
@media screen and (max-width:1000px) {
    .element { @include pageTemplateMargin(15px);}
}
@media screen and (max-width:800px) {
    .element { @include pageTemplateMargin(20px);}
}

There's also a way of mapping through sass objects, such as:

$breakpoints: (
  1200: 10px,
  1000: 15px,
  800: 20px,
);

@media screen and (max-width:1200px) {
    .element { margin-top: map-get($breakpoints, 1200);}
}
@media screen and (max-width:1000px) {
    .element { margin-top: map-get($breakpoints, 1000);}
}
@media screen and (max-width:800px) {
    .element { margin-top: map-get($breakpoints, 800);}
}

This would allow you to globally change the margin by adjusting 1 variable.

Working codepen example

回答3:

I have tried this then i fixed my issue. It will calculate all media-breakpoint automatically by given rate (base-size/rate-size)

$base-size: 16;
$rate-size-xl: 24;

    // set default size for all cases;
    :root {
      --size: #{$base-size};
    }

    // if it's smaller then LG it will set size rate to 16/16;
    // example: if size set to 14px, it will be 14px * 16 / 16 = 14px
    @include media-breakpoint-down(lg) {
      :root {
        --size: #{$base-size};
      }
    }

    // if it is bigger then XL it will set size rate to 24/16;
    // example: if size set to 14px, it will be 14px * 24 / 16 = 21px
    @include media-breakpoint-up(xl) {
      :root {
        --size: #{$rate-size-xl};
      }
    }

@function size($px) {
   @return calc(#{$px} / $base-size * var(--size));
}

div {
  font-size: size(14px);
  width: size(150px);
}