partial

gistfile1.txt

// partial
;(function() {

  var BASE_FONT_SIZE = 100;
  var zoom = partial(function( a, b ) {
    return a + b;
  }, BASE_FONT_SIZE );

  var result = zoom( -30 );     // 70
  var result2 = zoom( 50 );     // 150
  console.assert( result === 70 );
  console.assert( result2 === 150 );

})();