index.js
function(s1, s2, s5, val){
        return s1 ?
            [s1 + s2 + val, 'px' + s5].join(''):
            [s2 + val, 'px' + s5].join('');
    }
function(s1, s2, s5, val){
        return s1 ?
            [s1 + s2 + val, 'px' + s5].join(''):
            [s2 + val, 'px' + s5].join('');
    }
function ( s1 , s2 , s5 , val ) { return s1 ? [ s1 + s2 + val , 'px' + s5 ] . join ( '' ) : [ s2 + val , 'px' + s5 ] . join ( '' ) ; }
REM => PX
REM = > PX