Laura Fox

Laura Fox

1657059360

Nestjs Auth0 | A Template for using Auth0 with The Nest Framework

Description

A template for using Auth0 with the Nest framework. To start, either fork this repository or run

$ git clone --depth 1 https://github.com/jajaperson/nestjs-auth0.git

Setup

You'll need to populate a .env file with Auth0 configuration environemt details. This file should never be committed for obvious reasons (hence the reason it's .gitignore-d).

AUTH0_DOMAIN={your Auth0 domain}
AUTH0_CLIENT_ID={the Auth0 client ID for your app}
AUTH0_CLIENT_SECRET={the Auth0 client secret for your app}
AUTH0_AUDIENCE={http://localhost:3000 or your production domain accordingly}

A template .env file can be found at .env.example.

You may also like to remove all the irrelevant metadata from the package.json, suck as the repository, homepage, bugs, and description fields.

Installation

$ npm install

Running the app

# development
$ npm run start

# watch mode
$ npm run start:dev

# production mode
$ npm run start:prod

Test

# unit tests
$ npm run test

# e2e tests
$ npm run test:e2e

# test coverage
$ npm run test:cov

Explanation

Authentication logic

This template nest app uses the jwks-rsa package along with passport-jwt and @nestjs/passport for authentication. All authentication logic is in the /src/auth/ submodule.

src/auth/
├── auth.module.ts
├── interfaces
│   └── jwt-payload.interface.ts
├── jwt.strategy.spec.ts
└── jwt.strategy.ts

The JwtStrategy injectable contains all the core functionality, where the constructor sets up core token validation using the jwks-rsa library. All the Auth0 configuration for this is done in the .env file using @nestjs/config (see above). On any request with authentication, the decoded JSON web token (which should follow JwtPayload) is passed to the validate, which checks the token for the required scopes.

The AuthModule itself exports both PassportModule and the JwtStrategy injectable, and registers JwtStrategy as default.

AuthModule is imported by AppModule, and protected routes are decorated with @UseGuards(AuthGuard()) in AppController.

More info

See the Nest documentation.

Download Details:
Author: jajaperson
Source Code: https://github.com/jajaperson/nestjs-auth0
License: MIT license

#nestjs #node #javascript

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Nestjs Auth0 | A Template for using Auth0 with The Nest Framework
Chloe Butler

Chloe Butler

1667425440

Pdf2gerb: Perl Script Converts PDF Files to Gerber format

pdf2gerb

Perl script converts PDF files to Gerber format

Pdf2Gerb generates Gerber 274X photoplotting and Excellon drill files from PDFs of a PCB. Up to three PDFs are used: the top copper layer, the bottom copper layer (for 2-sided PCBs), and an optional silk screen layer. The PDFs can be created directly from any PDF drawing software, or a PDF print driver can be used to capture the Print output if the drawing software does not directly support output to PDF.

The general workflow is as follows:

  1. Design the PCB using your favorite CAD or drawing software.
  2. Print the top and bottom copper and top silk screen layers to a PDF file.
  3. Run Pdf2Gerb on the PDFs to create Gerber and Excellon files.
  4. Use a Gerber viewer to double-check the output against the original PCB design.
  5. Make adjustments as needed.
  6. Submit the files to a PCB manufacturer.

Please note that Pdf2Gerb does NOT perform DRC (Design Rule Checks), as these will vary according to individual PCB manufacturer conventions and capabilities. Also note that Pdf2Gerb is not perfect, so the output files must always be checked before submitting them. As of version 1.6, Pdf2Gerb supports most PCB elements, such as round and square pads, round holes, traces, SMD pads, ground planes, no-fill areas, and panelization. However, because it interprets the graphical output of a Print function, there are limitations in what it can recognize (or there may be bugs).

See docs/Pdf2Gerb.pdf for install/setup, config, usage, and other info.

pdf2gerb_cfg.pm

#Pdf2Gerb config settings:
#Put this file in same folder/directory as pdf2gerb.pl itself (global settings),
#or copy to another folder/directory with PDFs if you want PCB-specific settings.
#There is only one user of this file, so we don't need a custom package or namespace.
#NOTE: all constants defined in here will be added to main namespace.
#package pdf2gerb_cfg;

use strict; #trap undef vars (easier debug)
use warnings; #other useful info (easier debug)


##############################################################################################
#configurable settings:
#change values here instead of in main pfg2gerb.pl file

use constant WANT_COLORS => ($^O !~ m/Win/); #ANSI colors no worky on Windows? this must be set < first DebugPrint() call

#just a little warning; set realistic expectations:
#DebugPrint("${\(CYAN)}Pdf2Gerb.pl ${\(VERSION)}, $^O O/S\n${\(YELLOW)}${\(BOLD)}${\(ITALIC)}This is EXPERIMENTAL software.  \nGerber files MAY CONTAIN ERRORS.  Please CHECK them before fabrication!${\(RESET)}", 0); #if WANT_DEBUG

use constant METRIC => FALSE; #set to TRUE for metric units (only affect final numbers in output files, not internal arithmetic)
use constant APERTURE_LIMIT => 0; #34; #max #apertures to use; generate warnings if too many apertures are used (0 to not check)
use constant DRILL_FMT => '2.4'; #'2.3'; #'2.4' is the default for PCB fab; change to '2.3' for CNC

use constant WANT_DEBUG => 0; #10; #level of debug wanted; higher == more, lower == less, 0 == none
use constant GERBER_DEBUG => 0; #level of debug to include in Gerber file; DON'T USE FOR FABRICATION
use constant WANT_STREAMS => FALSE; #TRUE; #save decompressed streams to files (for debug)
use constant WANT_ALLINPUT => FALSE; #TRUE; #save entire input stream (for debug ONLY)

#DebugPrint(sprintf("${\(CYAN)}DEBUG: stdout %d, gerber %d, want streams? %d, all input? %d, O/S: $^O, Perl: $]${\(RESET)}\n", WANT_DEBUG, GERBER_DEBUG, WANT_STREAMS, WANT_ALLINPUT), 1);
#DebugPrint(sprintf("max int = %d, min int = %d\n", MAXINT, MININT), 1); 

#define standard trace and pad sizes to reduce scaling or PDF rendering errors:
#This avoids weird aperture settings and replaces them with more standardized values.
#(I'm not sure how photoplotters handle strange sizes).
#Fewer choices here gives more accurate mapping in the final Gerber files.
#units are in inches
use constant TOOL_SIZES => #add more as desired
(
#round or square pads (> 0) and drills (< 0):
    .010, -.001,  #tiny pads for SMD; dummy drill size (too small for practical use, but needed so StandardTool will use this entry)
    .031, -.014,  #used for vias
    .041, -.020,  #smallest non-filled plated hole
    .051, -.025,
    .056, -.029,  #useful for IC pins
    .070, -.033,
    .075, -.040,  #heavier leads
#    .090, -.043,  #NOTE: 600 dpi is not high enough resolution to reliably distinguish between .043" and .046", so choose 1 of the 2 here
    .100, -.046,
    .115, -.052,
    .130, -.061,
    .140, -.067,
    .150, -.079,
    .175, -.088,
    .190, -.093,
    .200, -.100,
    .220, -.110,
    .160, -.125,  #useful for mounting holes
#some additional pad sizes without holes (repeat a previous hole size if you just want the pad size):
    .090, -.040,  #want a .090 pad option, but use dummy hole size
    .065, -.040, #.065 x .065 rect pad
    .035, -.040, #.035 x .065 rect pad
#traces:
    .001,  #too thin for real traces; use only for board outlines
    .006,  #minimum real trace width; mainly used for text
    .008,  #mainly used for mid-sized text, not traces
    .010,  #minimum recommended trace width for low-current signals
    .012,
    .015,  #moderate low-voltage current
    .020,  #heavier trace for power, ground (even if a lighter one is adequate)
    .025,
    .030,  #heavy-current traces; be careful with these ones!
    .040,
    .050,
    .060,
    .080,
    .100,
    .120,
);
#Areas larger than the values below will be filled with parallel lines:
#This cuts down on the number of aperture sizes used.
#Set to 0 to always use an aperture or drill, regardless of size.
use constant { MAX_APERTURE => max((TOOL_SIZES)) + .004, MAX_DRILL => -min((TOOL_SIZES)) + .004 }; #max aperture and drill sizes (plus a little tolerance)
#DebugPrint(sprintf("using %d standard tool sizes: %s, max aper %.3f, max drill %.3f\n", scalar((TOOL_SIZES)), join(", ", (TOOL_SIZES)), MAX_APERTURE, MAX_DRILL), 1);

#NOTE: Compare the PDF to the original CAD file to check the accuracy of the PDF rendering and parsing!
#for example, the CAD software I used generated the following circles for holes:
#CAD hole size:   parsed PDF diameter:      error:
#  .014                .016                +.002
#  .020                .02267              +.00267
#  .025                .026                +.001
#  .029                .03167              +.00267
#  .033                .036                +.003
#  .040                .04267              +.00267
#This was usually ~ .002" - .003" too big compared to the hole as displayed in the CAD software.
#To compensate for PDF rendering errors (either during CAD Print function or PDF parsing logic), adjust the values below as needed.
#units are pixels; for example, a value of 2.4 at 600 dpi = .0004 inch, 2 at 600 dpi = .0033"
use constant
{
    HOLE_ADJUST => -0.004 * 600, #-2.6, #holes seemed to be slightly oversized (by .002" - .004"), so shrink them a little
    RNDPAD_ADJUST => -0.003 * 600, #-2, #-2.4, #round pads seemed to be slightly oversized, so shrink them a little
    SQRPAD_ADJUST => +0.001 * 600, #+.5, #square pads are sometimes too small by .00067, so bump them up a little
    RECTPAD_ADJUST => 0, #(pixels) rectangular pads seem to be okay? (not tested much)
    TRACE_ADJUST => 0, #(pixels) traces seemed to be okay?
    REDUCE_TOLERANCE => .001, #(inches) allow this much variation when reducing circles and rects
};

#Also, my CAD's Print function or the PDF print driver I used was a little off for circles, so define some additional adjustment values here:
#Values are added to X/Y coordinates; units are pixels; for example, a value of 1 at 600 dpi would be ~= .002 inch
use constant
{
    CIRCLE_ADJUST_MINX => 0,
    CIRCLE_ADJUST_MINY => -0.001 * 600, #-1, #circles were a little too high, so nudge them a little lower
    CIRCLE_ADJUST_MAXX => +0.001 * 600, #+1, #circles were a little too far to the left, so nudge them a little to the right
    CIRCLE_ADJUST_MAXY => 0,
    SUBST_CIRCLE_CLIPRECT => FALSE, #generate circle and substitute for clip rects (to compensate for the way some CAD software draws circles)
    WANT_CLIPRECT => TRUE, #FALSE, #AI doesn't need clip rect at all? should be on normally?
    RECT_COMPLETION => FALSE, #TRUE, #fill in 4th side of rect when 3 sides found
};

#allow .012 clearance around pads for solder mask:
#This value effectively adjusts pad sizes in the TOOL_SIZES list above (only for solder mask layers).
use constant SOLDER_MARGIN => +.012; #units are inches

#line join/cap styles:
use constant
{
    CAP_NONE => 0, #butt (none); line is exact length
    CAP_ROUND => 1, #round cap/join; line overhangs by a semi-circle at either end
    CAP_SQUARE => 2, #square cap/join; line overhangs by a half square on either end
    CAP_OVERRIDE => FALSE, #cap style overrides drawing logic
};
    
#number of elements in each shape type:
use constant
{
    RECT_SHAPELEN => 6, #x0, y0, x1, y1, count, "rect" (start, end corners)
    LINE_SHAPELEN => 6, #x0, y0, x1, y1, count, "line" (line seg)
    CURVE_SHAPELEN => 10, #xstart, ystart, x0, y0, x1, y1, xend, yend, count, "curve" (bezier 2 points)
    CIRCLE_SHAPELEN => 5, #x, y, 5, count, "circle" (center + radius)
};
#const my %SHAPELEN =
#Readonly my %SHAPELEN =>
our %SHAPELEN =
(
    rect => RECT_SHAPELEN,
    line => LINE_SHAPELEN,
    curve => CURVE_SHAPELEN,
    circle => CIRCLE_SHAPELEN,
);

#panelization:
#This will repeat the entire body the number of times indicated along the X or Y axes (files grow accordingly).
#Display elements that overhang PCB boundary can be squashed or left as-is (typically text or other silk screen markings).
#Set "overhangs" TRUE to allow overhangs, FALSE to truncate them.
#xpad and ypad allow margins to be added around outer edge of panelized PCB.
use constant PANELIZE => {'x' => 1, 'y' => 1, 'xpad' => 0, 'ypad' => 0, 'overhangs' => TRUE}; #number of times to repeat in X and Y directions

# Set this to 1 if you need TurboCAD support.
#$turboCAD = FALSE; #is this still needed as an option?

#CIRCAD pad generation uses an appropriate aperture, then moves it (stroke) "a little" - we use this to find pads and distinguish them from PCB holes. 
use constant PAD_STROKE => 0.3; #0.0005 * 600; #units are pixels
#convert very short traces to pads or holes:
use constant TRACE_MINLEN => .001; #units are inches
#use constant ALWAYS_XY => TRUE; #FALSE; #force XY even if X or Y doesn't change; NOTE: needs to be TRUE for all pads to show in FlatCAM and ViewPlot
use constant REMOVE_POLARITY => FALSE; #TRUE; #set to remove subtractive (negative) polarity; NOTE: must be FALSE for ground planes

#PDF uses "points", each point = 1/72 inch
#combined with a PDF scale factor of .12, this gives 600 dpi resolution (1/72 * .12 = 600 dpi)
use constant INCHES_PER_POINT => 1/72; #0.0138888889; #multiply point-size by this to get inches

# The precision used when computing a bezier curve. Higher numbers are more precise but slower (and generate larger files).
#$bezierPrecision = 100;
use constant BEZIER_PRECISION => 36; #100; #use const; reduced for faster rendering (mainly used for silk screen and thermal pads)

# Ground planes and silk screen or larger copper rectangles or circles are filled line-by-line using this resolution.
use constant FILL_WIDTH => .01; #fill at most 0.01 inch at a time

# The max number of characters to read into memory
use constant MAX_BYTES => 10 * M; #bumped up to 10 MB, use const

use constant DUP_DRILL1 => TRUE; #FALSE; #kludge: ViewPlot doesn't load drill files that are too small so duplicate first tool

my $runtime = time(); #Time::HiRes::gettimeofday(); #measure my execution time

print STDERR "Loaded config settings from '${\(__FILE__)}'.\n";
1; #last value must be truthful to indicate successful load


#############################################################################################
#junk/experiment:

#use Package::Constants;
#use Exporter qw(import); #https://perldoc.perl.org/Exporter.html

#my $caller = "pdf2gerb::";

#sub cfg
#{
#    my $proto = shift;
#    my $class = ref($proto) || $proto;
#    my $settings =
#    {
#        $WANT_DEBUG => 990, #10; #level of debug wanted; higher == more, lower == less, 0 == none
#    };
#    bless($settings, $class);
#    return $settings;
#}

#use constant HELLO => "hi there2"; #"main::HELLO" => "hi there";
#use constant GOODBYE => 14; #"main::GOODBYE" => 12;

#print STDERR "read cfg file\n";

#our @EXPORT_OK = Package::Constants->list(__PACKAGE__); #https://www.perlmonks.org/?node_id=1072691; NOTE: "_OK" skips short/common names

#print STDERR scalar(@EXPORT_OK) . " consts exported:\n";
#foreach(@EXPORT_OK) { print STDERR "$_\n"; }
#my $val = main::thing("xyz");
#print STDERR "caller gave me $val\n";
#foreach my $arg (@ARGV) { print STDERR "arg $arg\n"; }

Download Details:

Author: swannman
Source Code: https://github.com/swannman/pdf2gerb

License: GPL-3.0 license

#perl 

Laura Fox

Laura Fox

1657059360

Nestjs Auth0 | A Template for using Auth0 with The Nest Framework

Description

A template for using Auth0 with the Nest framework. To start, either fork this repository or run

$ git clone --depth 1 https://github.com/jajaperson/nestjs-auth0.git

Setup

You'll need to populate a .env file with Auth0 configuration environemt details. This file should never be committed for obvious reasons (hence the reason it's .gitignore-d).

AUTH0_DOMAIN={your Auth0 domain}
AUTH0_CLIENT_ID={the Auth0 client ID for your app}
AUTH0_CLIENT_SECRET={the Auth0 client secret for your app}
AUTH0_AUDIENCE={http://localhost:3000 or your production domain accordingly}

A template .env file can be found at .env.example.

You may also like to remove all the irrelevant metadata from the package.json, suck as the repository, homepage, bugs, and description fields.

Installation

$ npm install

Running the app

# development
$ npm run start

# watch mode
$ npm run start:dev

# production mode
$ npm run start:prod

Test

# unit tests
$ npm run test

# e2e tests
$ npm run test:e2e

# test coverage
$ npm run test:cov

Explanation

Authentication logic

This template nest app uses the jwks-rsa package along with passport-jwt and @nestjs/passport for authentication. All authentication logic is in the /src/auth/ submodule.

src/auth/
├── auth.module.ts
├── interfaces
│   └── jwt-payload.interface.ts
├── jwt.strategy.spec.ts
└── jwt.strategy.ts

The JwtStrategy injectable contains all the core functionality, where the constructor sets up core token validation using the jwks-rsa library. All the Auth0 configuration for this is done in the .env file using @nestjs/config (see above). On any request with authentication, the decoded JSON web token (which should follow JwtPayload) is passed to the validate, which checks the token for the required scopes.

The AuthModule itself exports both PassportModule and the JwtStrategy injectable, and registers JwtStrategy as default.

AuthModule is imported by AppModule, and protected routes are decorated with @UseGuards(AuthGuard()) in AppController.

More info

See the Nest documentation.

Download Details:
Author: jajaperson
Source Code: https://github.com/jajaperson/nestjs-auth0
License: MIT license

#nestjs #node #javascript

Solwin Infotech

Solwin Infotech

1620729846

Why Use WordPress? What Can You Do With WordPress?

Can you use WordPress for anything other than blogging? To your surprise, yes. WordPress is more than just a blogging tool, and it has helped thousands of websites and web applications to thrive. The use of WordPress powers around 40% of online projects, and today in our blog, we would visit some amazing uses of WordPress other than blogging.
What Is The Use Of WordPress?

WordPress is the most popular website platform in the world. It is the first choice of businesses that want to set a feature-rich and dynamic Content Management System. So, if you ask what WordPress is used for, the answer is – everything. It is a super-flexible, feature-rich and secure platform that offers everything to build unique websites and applications. Let’s start knowing them:

1. Multiple Websites Under A Single Installation
WordPress Multisite allows you to develop multiple sites from a single WordPress installation. You can download WordPress and start building websites you want to launch under a single server. Literally speaking, you can handle hundreds of sites from one single dashboard, which now needs applause.
It is a highly efficient platform that allows you to easily run several websites under the same login credentials. One of the best things about WordPress is the themes it has to offer. You can simply download them and plugin for various sites and save space on sites without losing their speed.

2. WordPress Social Network
WordPress can be used for high-end projects such as Social Media Network. If you don’t have the money and patience to hire a coder and invest months in building a feature-rich social media site, go for WordPress. It is one of the most amazing uses of WordPress. Its stunning CMS is unbeatable. And you can build sites as good as Facebook or Reddit etc. It can just make the process a lot easier.
To set up a social media network, you would have to download a WordPress Plugin called BuddyPress. It would allow you to connect a community page with ease and would provide all the necessary features of a community or social media. It has direct messaging, activity stream, user groups, extended profiles, and so much more. You just have to download and configure it.
If BuddyPress doesn’t meet all your needs, don’t give up on your dreams. You can try out WP Symposium or PeepSo. There are also several themes you can use to build a social network.

3. Create A Forum For Your Brand’s Community
Communities are very important for your business. They help you stay in constant connection with your users and consumers. And allow you to turn them into a loyal customer base. Meanwhile, there are many good technologies that can be used for building a community page – the good old WordPress is still the best.
It is the best community development technology. If you want to build your online community, you need to consider all the amazing features you get with WordPress. Plugins such as BB Press is an open-source, template-driven PHP/ MySQL forum software. It is very simple and doesn’t hamper the experience of the website.
Other tools such as wpFoRo and Asgaros Forum are equally good for creating a community blog. They are lightweight tools that are easy to manage and integrate with your WordPress site easily. However, there is only one tiny problem; you need to have some technical knowledge to build a WordPress Community blog page.

4. Shortcodes
Since we gave you a problem in the previous section, we would also give you a perfect solution for it. You might not know to code, but you have shortcodes. Shortcodes help you execute functions without having to code. It is an easy way to build an amazing website, add new features, customize plugins easily. They are short lines of code, and rather than memorizing multiple lines; you can have zero technical knowledge and start building a feature-rich website or application.
There are also plugins like Shortcoder, Shortcodes Ultimate, and the Basics available on WordPress that can be used, and you would not even have to remember the shortcodes.

5. Build Online Stores
If you still think about why to use WordPress, use it to build an online store. You can start selling your goods online and start selling. It is an affordable technology that helps you build a feature-rich eCommerce store with WordPress.
WooCommerce is an extension of WordPress and is one of the most used eCommerce solutions. WooCommerce holds a 28% share of the global market and is one of the best ways to set up an online store. It allows you to build user-friendly and professional online stores and has thousands of free and paid extensions. Moreover as an open-source platform, and you don’t have to pay for the license.
Apart from WooCommerce, there are Easy Digital Downloads, iThemes Exchange, Shopify eCommerce plugin, and so much more available.

6. Security Features
WordPress takes security very seriously. It offers tons of external solutions that help you in safeguarding your WordPress site. While there is no way to ensure 100% security, it provides regular updates with security patches and provides several plugins to help with backups, two-factor authorization, and more.
By choosing hosting providers like WP Engine, you can improve the security of the website. It helps in threat detection, manage patching and updates, and internal security audits for the customers, and so much more.

Read More

#use of wordpress #use wordpress for business website #use wordpress for website #what is use of wordpress #why use wordpress #why use wordpress to build a website

Nico Jonsson

Nico Jonsson

1605576444

How to Use DOM Manipulation properly in Angular

If you are coming from the background of working with angularjs, it was quite straight forward to access and manipulate the DOM there. You had access to the DOM node through element injected in the link function of the directive.

function link(scope, element, attrs) {
}

Or through angular.element which was an AngularJS’s built in subset of jQuery. But this approach had its drawbacks. It made your code tightly coupled with Browser’s API.

The new Angular (2 onwards) works on multiple platforms: mobile, web workers etc. So, they have introduced a number of APIs to work as an abstraction layer between your code and platform APIs. These APIs come in the form of different reference types likeElementRef, TemplateRef, ViewRef, ComponentRef and ViewContainerRef.

In this blog, we will see some examples of how these reference types can be used to manipulate DOM in angular. But before that let’s look at the ways to access these reference types within a Component/Directive.

DOM Queries

Angular has provided two ways to query/access various reference types within a Component/Directive. These are

  • ViewChild/ViewChildren
  • ContentChild/ContentChildren

ViewChild/ViewChildren

These are decorators which can be used within a Component/Directive as @ViewChild (returns a single reference) or @ViewChildren (returns a list of references in the form of a QueryList). These will assign the values of reference types from template to the component fields they are applied to. The basic usage is as follow:

@ViewChild(selector, {read: ReferenceType}) fieldName;

A selector can be a string representing a template reference variable, or a Component/Directive class, or a TemplateRef or a provider defined in the child component tree.

@ViewChild("myElem") template: ElementRef;

The second parameter is optional and is only required to query some reference types which can’t be inferred easily by Angular like ViewContainerRef.

@ViewChild("myContainer", {read: ViewContainerRef}) container: ViewContainerRef;

ContentChild/ContentChildren

The usage is pretty much similar to that of ViewChild/ViewChildren. The only difference is that it queries within the <ng-content> projected elements of the component while the @ViewChild queries within the template of the component. This will be explained better in the examples of upcoming sections.

DOM access via ElementRef

ElementRef is a very basic abstraction layer on a DOM element in Angular. It’s an angular wrapper around the native element.

You can get hold of ElementRef in a Component or Directive in following ways:

Dependency Injection

Host element of a Component or Directive can be accessed via direct DI in the constructor.

@Component({
  selector: 'app-test',
  template: '<div>I am a test component</div>'
})
export class TestComponent implements OnInit {

  constructor(private element: ElementRef) { }

  ngOnInit() {
    console.log(this.element.nativeElement);
  }

}
/*
* Output: 
*   <app-test>
*     <div>I am a test component</div>
*   </app-test>
* */

Using ViewChild and Template Reference Variables

@Component({
  selector: 'app-test',
  template: `
    <div #child1>First Child</div>
    <div>Second Child</div>
  `
})
export class TestComponent implements OnInit {

  @ViewChild("child1") firstChild: ElementRef;

  constructor() { }

  ngOnInit() {
    console.log(this.firstChild.nativeElement);
  }

}

/*
* Output: <div>First Child</div>
* */

Using ContentChild

Works in a similar manner as that of @ViewChild, but for <ng-content> projected elements.

// Child Component
@Component({
  selector: "component-a",
  template: `<ng-content></ng-content>`
})
export class ComponentA {
  @ContentChild("contentChild") contentChild: ElementRef;
  
  ngOnInit() {
    console.log(this.contentChild.nativeElement);
  }
}
// Parent Component
@Component({
  selector: 'app-test',
  template: `
    <component-a>
      <div #contentChild>Content Child 1</div>
      <div>Content Child 2</div>
    </component-a>
  `
})
export class TestComponent implements OnInit {}
/*
* Output: <div>Content Child 1</div>
* */

It looks pretty straight forward that you can easily access a DOM element via ElementRef and then manipulate the DOM by accessing the nativeElement. Something like this:

@Component({
  selector: 'app-test-component',
  template: `
    <div class="header">I am a header</div>
    <div class="body" #body>
    </div>
    <div class="footer">I am a footer</div>
  `
})
export class TestComponent implements AfterContentInit {
  @ViewChild("body") bodyElem: ElementRef;

  ngAfterContentInit(): void {
    this.bodyElem.nativeElement.innerHTML = `<div>Hi, I am child added by directly calling the native APIs.</div>`;
  }

}

However, the direct usage of ElementRef is discouraged by Angular Team because it directly provides the access to DOM which can make your application vulnerable to XSS attacks. It also creates tight coupling between your application and rendering layers which makes is difficult to run an app on multiple platforms.

Everything is a ‘View’ in Angular

A view is the smallest building block of an angular app’s UI. Every component has its own view. You can consider it as a group of elements which can be created and destroyed together.

A view can be classified into two types:

  • Embedded Views — created from templates
  • Host Views — created from components

Displaying a view in UI can be broken down into two steps:

  1. Creating a view from template or component
  2. Rendering a view into a view container

Embedded Views

Embedded views are created from templates defined using <ng-template> element.

Creating an embedded view

First a template needs to be accessed within a component as TemplateRefusing @ViewChild and template reference variable. Then, an embedded view can be created from a TemplateRef by passing a data-binding context.

const viewRef = this.template.createEmbeddedView({
  name: "View 1"
});

This context is being consumed by the template in<ng-template>.

<ng-template #template let-viewName="name">
  <div>Hi, My name is {{viewName}}. I am a view created from a template</div>
</ng-template>

You can also use the $implicit property in the context if you have only a single property to bind.

const viewRef = this.template.createEmbeddedView({
  $implicit: "View 1"
});

In this case, you can skip assigning values to template variables.

<ng-template #template let-viewName>
  <div>Hi, My name is {{viewName}}. I am a view created from a template</div>
</ng-template>

Rendering an embedded view

Till now, we have created only an instance of ViewRef. This view is still not visible in the UI. In order to see it in the UI, we need a placeholder (a view container) to render it. This placeholder is being provided by ViewContainerRef.

Any element can serve as a view container, however <ng-container> is a better candidate as it is rendered as a comment and doesn’t leave any redundant element in the html DOM.

@Component({
  selector: 'app-test-component',
  template: `
    <div class="header">I am a header</div>
    <div class="body">
      <ng-container #container></ng-container>
    </div>
    <div class="footer">I am a footer</div>

    <ng-template #template let-viewName="name">
      <div>Hi, My name is {{viewName}}. I am a view created from a template</div>
    </ng-template>
  `,
})
export class TestComponent implements AfterContentInit {

  @ViewChild("template") template: TemplateRef;
  @ViewChild("container", {read: ViewContainerRef}) container: ViewContainerRef;

  constructor() { }

  ngAfterContentInit(): void {
    const viewRef = this.template.createEmbeddedView({
      name: "View 1"
    });
    this.container.insert(viewRef);
  }
}

Both <ng-container> and <ng-template> elements will be rendered as comments leaving the html DOM neat and clean.

The above 2 steps process of creating a view and adding it into a container can further be reduced by using the createEmbeddedView method available in the ViewContainerRef itself.

this.container.createEmbeddedView(this.template, {
  name: "View 1"
});

This can be further simplified by moving the whole view creation logic from component class to the template using ngTemplateOutlet and ngTemplateOutletContext.

@Component({
  selector: 'app-test-component',
  template: `
    <div class="header">I am a header</div>
    <div class="body">
      <ng-container [ngTemplateOutlet]="template" [ngTemplateOutletContext]="{name: 'View 1'}"></ng-container>
    </div>
    <div class="footer">I am a footer</div>

    <ng-template #template let-viewName="name">
      <div>Hi, My name is {{viewName}}. I am a view created from a template</div>
    </ng-template>
  `
})
export class TestComponent {}

Host Views

Host Views are quite similar to Embedded View. The only difference is that the Host Views are created from components instead of templates.

Creating a host view

In order to create a host view, first you need to create a ComponentFactory of the component you want to render using ComponentFactoryResolver.

constructor(
  private componentFactoryResolver: ComponentFactoryResolver
) {
  this.someComponentFactory = this.componentFactoryResolver.resolveComponentFactory(SomeComponent);
}

Then, a dynamic instance of the component is created by passing an Injector instance to the factory. Every component should be bound to an instance of Injector. You can use the injector of the parent component for the dynamically created components.

const componentRef = this.someComponentFactory.create(this.injector);
const viewRef = componentRef.hostView;

Rendering a host view

Rendering a host view is almost similar to rendering an embedded view. You can directly insert it into a view container.

@Component({
  selector: 'app-test-component',
  template: `
    <div class="header">I am a header</div>
    <div class="body">
      <ng-container #container></ng-container>
    </div>
    <div class="footer">I am a footer</div>
  `,
})
export class TestComponentComponent implements AfterContentInit {

  @ViewChild("container", {read: ViewContainerRef}) container: ViewContainerRef;

  private someComponentFactory: ComponentFactory<SomeComponent>;

  constructor(
    private componentFactoryResolver: ComponentFactoryResolver,
    private injector: Injector
  ) {
    this.someComponentFactory = this.componentFactoryResolver.resolveComponentFactory(SomeComponent);
  }

  ngAfterContentInit(): void {
    const componentRef = this.someComponentFactory.create(this.injector);
    const viewRef = componentRef.hostView;
    this.container.insert(viewRef);
  }
}

Or by directly calling the createComponent method of ViewContainerRef and passing the component factory instance.

this.container.createComponent(this.someComponentFactory);

Now, similar to embedded view, we can also shift the whole logic of host view creation in template itself using ngComponentOutlet.

@Component({
  selector: 'app-test-component',
  template: `
    <div class="header">I am a header</div>
    <div class="body">
      <ng-container [ngComponentOutlet]="comp"></ng-container>
    </div>
    <div class="footer">I am a footer</div>
  `
})
export class TestComponent {
  comp = SomeComponent;
}

Don’t forget to store the reference of the component class in parent component’s field. The template has access only to the fields of the components.

Summary

Here we come to an end. Let’s conclude what we have understood till now.

  • We can access the DOM in Angular using different reference types likeElementRef, TemplateRef, ViewRef, ComponentRef and ViewContainerRef.
  • These reference types can be queried from templates using @ViewChild and @ContentChild.
  • Browser’s native DOM element can be accessed via ElementRef. However, manipulating this element directly is discouraged because of security reasons.
  • Concept of Views.
  • How to create and render an Embedded View.
  • How to create and render a Component View.

So, that’s it for today about understanding DOM manipulation in Angular.

Originally published by medium

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