How to use Angular’s ngIf directive

How to use Angular’s ngIf directive

Angular comes standard with a directive called ngIf directive.

It is a simple if statement, and its usage is to display if the if statement is true.

The way to describe it is as follows.

dell.component.html

<div *ngIf='flg'>
  <p>{{flg}}</p>
</div>

dell.component.ts

import { Component, OnInit } from '@angular/core';

@Component({
selector: 'app-dell',
templateUrl: './dell.component.html',
styleUrls: ['./dell.component.css']
})
export class DellComponent implements OnInit {

constructor() { }
flg = true;
ngOnInit() {
}
}

flg = true; so the div tag is visible.

Angular のngIf ディレクティブの使い方

Since Angular4, ngIf~else statements can be written.

dell.component.html

<div *ngIf='flg; else Statement'> <!-- Note the enclosed area. -->
  <p>{{flg}}</p>
</div>
<ng-template #Statement>
  <p>else文です</p>
</ng-template>

If flg is set to false, the following is displayed.

Angular のngIf ディレクティブの使い方

boolean型でない場合の挙動

The variable part of ngIf='variable' is not necessarily of type boolean.

I checked for cases where the behavior is false.

結果
true true
false false
null false
undefined false
[] true
{} true
0 false
1 true
-1 true

To use ngIf, the following must be imported in app.module.ts

import { FormsModule } from '@angular/forms';

imports [
  BrowserModule,
  FormsModule
]

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