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Trying out the New Angular 4 If Else Conditionals

By Gary simon - Mar 13, 2017

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Now that Angular 4 is officially here, I thought it would be worth taking a look at one of the more exciting and usable features: If Else conditionals.

This will make life a bit easier and more structured when dealing with conditionals in the template.

 First, if you prefer watching a video tutorial..

I've recorded a video tutorial that outlines everything below. Be sure to subscribe to the channel for more awesome videos!

 Starting an Angular 4 Project

With the release of the first stable version of the Angular CLI, it installs an Angular 4 project by default. So, first, run:

> ng -v

If it goes unrecognized, or if the @angular/cli version is not 1.0.0, then you must use npm to install or upgrade the CLI:

> npm install -g @angular/cli

 

Once it's complete, you can start a new Angular 4 project by running:

> ng new ifelse-proj
> cd ifelse-proj

Then run the following command and open up localhost:4200 in the browser:

> ng serve

 A Simple If Else Statement in Angular 4

In Angular 2, you were unable to specify an else statement after an if. But now with Angular 4, we can!

First, open up /src/app/app.component.ts:

export class AppComponent {
  title = 'app works!';
}

Notice within the exported class AppComponent, we have a property that the angular-cli generates automatically called title. We'll use this title property for the basis of our if/else statements going forward.

Let's open up the /src/app/app.component.html file in the same folder and write the following code:

<div *ngIf="title; else login">
    The user is logged in.
</div>
<ng-template #login>Please login to continue.</ng-template>

The very first line is saying, "If the title property exists, then show this current div and anything inside of it. Otherwise (else) show the ng-template named #login.

So, if we're to assume the title property is checking a user's logged in state, then this is how you could tackle such a scenario. 

You can also use operators. Try changing the *ngIf to:

<div *ngIf="!title; else login">

And then try changing it to:

<div *ngIf="title == 'app works!'; else login">

Simple, huh?

 If Then Example

We can also use an if then statement within our Angular 4 templates. Try changing the HTML to the following:

<div *ngIf="title; then logout else login"></div>

<ng-template #login>Please login to continue.</ng-template>
<ng-template #logout>Hi Gary, <button>Logout now</button>.</ng-template>

This way, you can define templates for properties that are true!

If we want to give this some interactivity, change the last line of the HTML example above, to:

<ng-template #logout>Hi Gary, <button (click)="logMeIn()">Logout now</button>.</ng-template>

Then, inside app.component.ts add the logMeIn function:

export class AppComponent {
  title:any = true;

  logMeIn() {
    this.title = false;
  }
}

Now, in the browser you can click on the logout now button and it will show the other template.

And there you have it!

This will make our lives quite a bit easier as designers and developers. Be sure to browse around Coursetro for more Angular 4 related content which I will be sure to add!


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