@angular-extensions/pretty-html-log

Improved debugging of Angular component tests with Jest!

The @angular-extension/pretty-html-log is a module that makes debugging component tests with Jest a breeze. It adds a phl method which pretty prints the innerHTML of a ComponentFixture, a DebugElement, a NativeElement or an HTML string.

• Why you should use this module
• Features
• Getting started
  • Installation
  • Usage
• API
• Examples
  • Pass in specific DebugElement
  • Examples
  • Print Angular comments
  • Change the theme
• Further resources
  • Blog post
  • Video tutorial

Why you should use this module

When debugging component tests, it’s often necessary to inspect the DOM. The most common approach to do so is by using the good old console.log which has some downsides.

First of all, it’s annoying to always type

fixture.debugElement.nativeElement.innerHTML;

Moreover, the console.log statement doesn’t print the HTML in a very readable way. Therefore we still need to copy the string in a new HTML file and format it to be able to inspect it. Not with @angular-extensions/pretty-html-log!

Features

• Provides a phl method that highlights and pretty prints a fixture, debugElement, nativeElement or even a plain HTML string - you don't have to worry how to get to the HTML, just pass the thing you want to print to the phl method.
• in case you are using prettier (which you should ;)), pretty-html-log will pick up your prettier config and pretty print the HTML string based on your prettier configuration. 🤩

Getting started

Installation

This module will only be used during development and can therefore be installed as a dev dependency.

npm i -D @angular-extensions/pretty-html-log

Usage

The @angular-extensions/pretty-html-log package provides a phl method that you can use to pretty print a fixture, debugElement, nativeElement or even a plain HTML string. Simply import it while debugging and pretty print that HTML.

import { phl } from '@angular-extensions/pretty-html-log';

describe('my test suite', () => {
  it('should be green', () => {
    phl(fixture); // This will pretty print the fixture
    expect(myTable.getRows()).toBe(5);
  });
});

Note that this way adds a import method. To make sure this import statement gets cleaned up we should configure our eslint to clean up unused imports. More: https://www.npmjs.com/package/eslint-plugin-unused-imports.

API

The phl method has the following signature:

<T>(
  ngHTMLElement: NgHTMLElement<T>,
  enableComments = false,
  theme = THEMES.DRACULA
)

Property	Description
ngHTMLElement	Value to extract the html from and pretty print it to the console: ComponentFixture
enableComments (default: false)	When set to true we print the generated comments by Angular. For example: <!--bindings={"ng-reflect-ng-for-of":...
theme: (default: DRACULA)	pretty-html-log themes (DRACULA, VSCODE and MATERIAL)

Examples

Pass in specific DebugElement

In your test you can simply write the following line.

phl(fixture.debugElement.query(By.css('mat-tab-body')));

Which will print the following string to your console. Depending on your test configuration you might run into an issue with the patch of the console. In such cases its best to report an issue and use the logNgHTML function directly.

phl(fixture.debugElement.query(By.css('mat-tab-body')));

Examples

Log the content innerHTML of a fixture

phl(fixture);

of a debugElement (or multiple debugElements)

phl(fixture.debugElement);

of a nativeElement (or multiple nativeElements)

phl(fixture.debugElement.nativeElement);

or even a simple HTML string

phl('<h1>Foo</h1>');

Print Angular comments

Angular adds some comments to our HTML file. Usually, when debugging our tests, we don't need them. Therefore they are not printed by default. However, there are cases where you want to print those comments. To do so, you can pass true as an additional flag tot he logNgHTML method.

phl(fixture, true);

Change the theme

@angular-extensions/pretty-html-log allows you to print the html logs in different themes. Currently, we support (DRACULA, VSCODE and MATERIAL). The themes can be importet from pretty-html-log, the base library @angular-extensions/pretty-html-log depends on.

import { THEMES } from 'pretty-html-log';

console.logNgHTML(fixture, false, THEMES.VSCODE);

Further resources

Blog post

Improved debugging of Angular component tests in Jest is a write up on AngularInDepth that shows how @angular-extensions/pretty-html-log is used and set up in a project.

Video tutorial