We will learn how to convert variable arguments by using rest operator in JavaScript.

.sass-btn {
  color: #fff;
  background-color: #0069d9;
  margin: 5px;
  @include button-size();
  @include box-shadow(0px 4px 5px #666, 2px 6px 10px #999);
}

@mixin box-shadow($shadows...) {
  -moz-box-shadow: $shadows;
  
 
-webkit-box-shadow: $shadows;
  box-shadow: $shadows;
}

Scss "$shadows..." the same as "...shadows" in Javascript.

export const boxShadow = (...shadows) => `
  -moz-box-shadow: ${shadows};
  -webkit-box-shadow: ${shadows};
  box-shadow: ${shadows};
`

interesting thing is ...shadows in Javascript is an Array, but if we put into ${}, then it conver to a string:

const shadows = [‘red‘, ‘blue‘];

console.log(`${shadows}`); // red, blue

[SCSS] Convert SCSS Variable Arguments to JavaScript