The event handler in the previous section sets the property collapsed to false but that does not modify the template. In normal code, we would have written if (this.collapsed) { ... }. In templates, we cannot use that, but we can use ngIf.
A directive is an extension to normal HTML tags and attributes. It can define custom behavior. A custom component, such as the About page, can be seen as a directive too. The ngIf condition is a built-in directive in Angular. It is a custom attribute that displays the content if the specified value is true.
If a piece of a component needs to be shown a variable an amount of times, you can wrap it in a template tag. Using the ngIf (or ngFor) directive, you can control how often it is shown (in case of ngIf, once or zero times). The template tag will look like this:
<template [ngIf]="collapsed"> <div>Content</div> </template>
You can abbreviate this as follows...