Generated by SassMeister.com.

SassMeister-input.scss

// ----
// libsass (v3.2.4)
// ----

$bodyclass: '.bodyclass';

@mixin classmerge{
  $selector-list: &;
  
  @each $selector in $selector-list {
    $others: ();

    // Just html class - .htmlclass
    $htmlclass: nth($selector, 1);
    
    // If more than one element
    @if(length($selector)>1){
      @for $i from 2 through length($selector) {
        // Add the other selectors
        $others: append($others, nth($selector, $i), space);
      }
    }
    
    @at-root{
      /*! This should produce:
    .js .bodyclass .element .active */
      #{$htmlclass} {
        #{unquote($bodyclass)} {
          #{$others} {
            @content;
          }
        }
      }
    }
    
    
    @at-root{
      /*! (HACK) This fixes it though, but just for this case */
      html{
        &#{$htmlclass} {
          #{unquote($bodyclass)} {
            #{$others} {
              @content;
            }
          }
        }
      }
    }
  }  
}

.js{
  .element{
    .active{
      color: blue;
      
      @include classmerge {
        background: red;
      }
    }
  }
}

SassMeister-output.css

.js .element .active {
  color: blue;
}

/*! This should produce:
    .js .bodyclass .element .active */
.js .element .active .js .bodyclass .element .active {
  background: red;
}

/*! (HACK) This fixes it though, but just for this case */
html.js .bodyclass .element .active {
  background: red;
}