Debugging Like a Boss in Angular 9

Anthony Humes

This is going to rock!

What happens next?

Why did this happen?

When critical production issues arose, it was hard to debug them effectively costing time and resources

What can we learn?

to build good apps, you must be able to debug them effectively

to debug effectively, you must be able to use all of your available tools

New API in Angular 9

Comes directly from Ivy internal methods

Where can I access the new methods?

// Global variable in the console
ng

{
  getComponent: ƒ getComponent(element),
  getContext: ƒ getContext(element),
  getListeners: ƒ getListeners(element),
  getOwningComponent: ƒ getOwningComponent(elementOrDir),
  getHostElement: ƒ getHostElement(componentOrDirective),
  getInjector: ƒ getInjector(elementOrDir),
  getRootComponents: ƒ getRootComponents(elementOrDir),
  getDirectives: ƒ getDirectives(element),
  applyChanges: ƒ applyChanges(component)
}

Before we start...what is $0?

$0

<p class="some-element"></p>
<div class="some-div">
  <p class="some-element">
    Hey there text!
  </p>
</div>

most recent selection from the Elements Inspector or from using Inspect Element

Get Angular Elements

ng.getComponent

ng.getDirectives

ng.getListeners

ng.getComponent

ng.getDirectives

ng.getListeners

retrieves the component from an HTML element

retrieves an array of directives from an HTML element

returns an array of both html (ex. click) and host listeners for an HTML element

ng.getComponent

<app-parent class="some-div">
  <app-child class="some-element">
    Hey there text!
  </app-child>
</app-parent>
ng.getComponent($0)

ChildComponent {...}

ng.applyChanges

let component = ng.getComponent($0)

component.value = 10;

ng.applyChanges($0)
<app-element class="some-div">
  <p class="some-element">
    5
  </p>
</app-parent>
<app-element class="some-div">
  <p class="some-element">
    10
  </p>
</app-parent>

triggers change detection for the component or directive

ng.getOwningComponent

ng.getContext

ng.getOwningComponent

returns the parent component for the HTML element

ng.getContext

returns the context of an *ngIf or *ngFor for the HTML element

Other Methods

ng.getRootComponents

ng.getInjector

What these APIs won't do?

  • Replace using breakpoints in Chrome
  • Debug interactions between components
  • Debug complex state issues with Observables or NgRx
  • Magically fix every problem in your app

Note from the Angular Team

The current API is a work in process.  These methods are the starting point to a way more powerful set of debug tools than ng.probe.  More methods and better functionality will be coming in the future.

Demo

Next Steps

  • Experiment with the new methods
  • Spend some time pair programming with another developer
  • Help someone in the community with a problem they can't solve
  • Always keep learning!

Thank You!

Debugging Like a Boss in Angular 9

By Anthony Humes

Debugging Like a Boss in Angular 9

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