Angular2+: ng-template

This is an angular element which is used to render HTML, it never gets displayed directly. It is used by structural directives like ngIf and ngFor.

We can use them directly in some cases e.g when we want to reuse a template multiple times in our code. Suppose we have following code

<ng-template>
  <p>Hello World!</p>
</ng-template> 

 When it will run the code inside it will not get displayed. If you will inpect the HTML in your developer console you will see that the above will get replaced by a comment and you will find only following in its place.

<!---->

Now this doesn't make sense that angular is giving a component which just eats up your code and does nothing. This component is actually used to create a reusable template which can be accessd via a tempalte reference. It is used internally by angular to replace the structure directives with it and later at run time is converted into a comment. So for example if you have an ngFor in your code, it will be replaced by ng-template and at run time with a comment.

<div *ngfor="let i of [1,2,3,4,5,6]">
  <p>Hello World!</p>
</div>  

When you examin it in developer tools you will find the following

<!--bindings={
  "ng-reflect-ng-for-of": "1,2,3,4,5,6"
}-->

Now ngIf and ngFor both can be written in many different ways. We usually use compact syntax *ngIf and *ngFor to keep our code compact. Following are some examples of how we can write ngIf.

<div *ngIf="condition">...</div>
<div template="ngIf condition">...</div>
<ng-template [ngIf]="condition"><div>...</div></ng-template>

From the above, the third one is the form in which angular converts all our *ngIf block. So your first ngIf will converted like the following

<ng-template [ngIf]="condition">
  <div>...</div>
</ng-template>

As said previously in this post that ng-template can also be used to write your own reuseable templates. So how do we do that? You can define any block as ng-template and give it and id and refer to it using that id. Following is an example

<div *ngIf="condition; else elseBlock">...</div>
<ng-template #elseBlock>...</ng-template> 

Notice the id elseBlock in the ng-template directive and its use inside in ngIf value.