===== ngIf =====
Html Element를 보여주거나 안 보여주거나 한다.
<code javascript>
<div *ngIf="false">
  Codevolution
</div>
</code>
2.ng-template사용
<code javascript>
<div *ngIf="displayName; else elseBlock">
  Codevolution
</div>
<ng-template #elseBlock>
  <h2>
    name is hidden
  </h2>
</ng-template>
</code>
3.thenBlock사용
<code javascript>
<div *ngIf="displayName; then thenBlock; else elseBlock"></div>
<ng-template #thenBlock>
  <h2>Codevolution</h2>
</ng-template>
<ng-template #elseBlock>
  <h2>
    name is hidden
  </h2>
</ng-template>
</code>