What is going on on line 1 and 2? Why didn't we write anything inside the curly braces on line 2?

var SequenceSum = (function() {
  function SequenceSum() {}

  SequenceSum.showSequence = function(count) {
    var holder = [];
    for ( var i = 0; i <= count; i++){
      holder.push(i);
    }
    var a = holder.reduce(function(a, b){
      return a + b;
    })
    return a;
  };

  return SequenceSum;

})();
console.log(SequenceSum.showSequence(6))

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