Category: Angular

Debugging with the JSON pipe

Alain Chautard

We have all used console.log at some point to debug our code. With Angular, there is an interesting alternative to display debugging information on our web page temporarily: The JSON pipe.

The primary usage is as follows:

<span>myData | json</span>Code language: HTML, XML (xml)

The above code will output your data as a JSON string in the span element, but it won’t be formatted, so the JSON string can be hard to read:

{"affiliation":"friendly","symbol":"Default Land Unit","echelon":"none","mod1":"None","mod2":"None","uniqueDesignation":"","higherFormation":"","reinforcedReduced":"","flying":false,"activity":false,"installation":false,"taskForce":false,"commandPost":"None","tacticalMissionTasks":"None","type":"Land Unit"}Code language: JavaScript (javascript)

Instead, the following syntax works a lot better:

<pre>myData | json</pre>Code language: HTML, XML (xml)

The pre HTML tag stands for “preformatted” content. As a result, that tag will preserve any whitespace, new lines, and tabs, which makes reading that JSON data a lot easier:

{
 "affiliation":"friendly",
 "symbol":"Default Land Unit",
 "echelon":"none",
 "mod1":"None",
 "mod2":"None"
}Code language: JavaScript (javascript)

It’s a simple trick, yet a big time saver when debugging code that’s using complex JSON structures.

Exported Directives

Alain Chautard

Yesterday, we talked about Template Reference Variables. Today, I want to show you how a directive can be accessed with a Template Reference Variable.

You’ve probably seen that syntax before:

<form #myForm="ngForm" (ngSubmit)="onSubmit(myForm)" >Code language: HTML, XML (xml)

That syntax is possible because the NgForm directive is exported using the following syntax (actual Angular source code here):

@Directive({
   exportAs: 'ngForm'
})Code language: TypeScript (typescript)

The above code enables the usage of Template Reference Variables such as #myForm="ngForm" . This technique is widely used in Angular forms and component libraries to expose public directive properties (and methods) to your component’s template.

For instance, we can access myForm.value or myForm.valid in an expression.

ngModel is exported that way, too.

Template Reference Variables

Alain Chautard

Welcome to the very first edition of my daily Angular Newsletter! As promised, I’ll keep it nice and short.


Today’s topic is Template Reference variables. I usually call that feature “the hashtag syntax” because that’s how it’s used:

<input #phone placeholder="phone number" />Code language: HTML, XML (xml)

Here’s how I could use that reference variable to get the value of the input, for instance:

<button (click)="callPhone(phone.value)">Call</button>Code language: HTML, XML (xml)

phone refers to the input element with the #phone attribute created earlier. That’s the template reference variable.
These variables can be used instead of ngModel, for instance. Even better, they also work with components and directives!

For instance, the following template reference variable hello would have access to all public properties and methods of the HelloComponent:

<app-hello #hello ></app-hello>Code language: HTML, XML (xml)

For more information and examples, you can read another short blog post of mine here.