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SASS | negative variable value
  • Last Updated : 26 Mar, 2020

SASS variables are quite useful in writing maintainable styling code for web pages. Often, we require different components of a page to have the same value for a stylistic property. In such a scenario, assigning the value to a variable and using it wherever required reduces the amount of effort needed to make changes to the styling in the future. We might also require the negation of a variable’s value for a property sometimes. For instance, consider the SASS code given below:




$marg: 20px;
  
#div1 {
    margin: 0 20px 0 -20px;
}

The property values 20px and -20px can be substituted with the $marg variable. The obvious way to go about this would be:




$marg: 20px;
  
#div1 {
    margin: 0 $marg 0 -$marg;
}

However, on compilation, this generates the following css:




$marg: 20px;
  
#div1 {
    margin: 0 20px -20px;
}

This is because the SASS compiler treats 0 -$marg as a subtraction operation and outputs -20px. Hence, whenever we wish to use the negation of a variable, it might lead to undesirable output CSS, since the SASS compiler might mistake the intent to be binary subtraction.

Now there are multiple ways in which this problem can be solved.



  1. Using parenthesis: Enclosing the variable with a parenthesis will prevent the compiler from performing subtraction.




    $marg: 20px;
      
    #div1 {
        margin: 0 $marg 0 (-$marg);
    }
  2. Performing multiplication with a negative number: Simply multiplying the variable with -1 will generate its negation, while retaining its original units.




    $marg: 20px;
      
    #div1 {
        margin: 0 $marg 0 -1*$marg;
    }
  3. Using interpolation: Interpolating a value converts it into an unquoted string. It can be used to obtain the negation of a variable’s value. However, this is not recommended since the unquoted string in the output CSS will look like a number, but not work with numerical operators and functions, which can lead to misleading code.




    $marg: 20px;
      
    #div1 {
        margin: 0 $marg 0 -#{$marg};
    }

In all the above approaches, the following CSS is obtained on compilation:

#div1 {
    margin: 0 20px 0 -20px;
}

In this way, we can utilize a SASS variable for both positive and negative use cases, hence promoting variable reuse and more maintainable code.

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