Angular markdown component/directive/pipe/service to parse static, dynamic or remote content to html with syntax highlight
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ngx-markdown

ngx-markdown is an Angular library that uses marked to parse markdown to html combined with Prism.js for syntax highlight.

Table of contents

Installation

ngx-markdown

To add ngx-markdown library to your package.json use the following command.

npm install ngx-markdown --save

As the library is using marked parser you will need to add node_modules/marked/lib/marked.js to your application.

If you are using Angular CLI you can follow the angular.json example below...

"scripts": [
+ "node_modules/marked/lib/marked.js"
]

Syntax highlight

🔔 Syntax highlight is optional, skip this step if you are not planning to use it

To activate Prism.js syntax highlight you will need to include...

  • prism.js core library - node_modules/prismjs/prism.js file
  • a highlight css theme - from node_modules/prismjs/themes directory
  • desired code language syntax files - from node_modules/prismjs/components directory

Additional themes can be found by browsing the web such as Prism-Themes or Mokokai for example.

If you are using Angular CLI you can follow the angular.json example below...

"styles": [
  "styles.css",
+ "node_modules/prismjs/themes/prism-okaidia.css"
],
"scripts": [
+ "node_modules/prismjs/prism.js",
+ "node_modules/prismjs/components/prism-csharp.min.js", # c-sharp language syntax
+ "node_modules/prismjs/components/prism-css.min.js" # css language syntax
]

Configuration

Main application module

You must import MarkdownModule inside your main application module (usually named AppModule) with forRoot to be able to use markdown component and/or directive.

import { NgModule } from '@angular/core';
+ import { MarkdownModule } from 'ngx-markdown';

import { AppComponent } from './app.component';

@NgModule({
  imports: [
+   MarkdownModule.forRoot(),
  ],
  declarations: [AppComponent],
  bootstrap: [AppComponent],
})
export class AppModule { }

If you want to use the [src] attribute to directly load a remote file, in order to keep only one instance of HttpClient and avoid issues with interceptors, you also have to provide HttpClient:

imports: [
+  HttpClientModule,
+  MarkdownModule.forRoot({ loader: HttpClient }),
],

MarkedOptions

Optionaly, markdown parsing can be configured by passing MarkedOptions to the forRoot method of MarkdownModule.

Imports:

import { MarkdownModule, MarkedOptions } from 'ngx-markdown';

Default options:

// using default options
MarkdownModule.forRoot(),

Custom options and passing HttpClient to use [src] attribute:

// using specific options with ValueProvider and passing HttpClient
MarkdownModule.forRoot({
  loader: HttpClient, // optional, only if you use [src] attribute
  markedOptions: {
    provide: MarkedOptions,
    useValue: {
      gfm: true,
      tables: true,
      breaks: false,
      pedantic: false,
      sanitize: false,
      smartLists: true,
      smartypants: false,
    },
  },
}),

MarkedOptions.renderer

MarkedOptions also exposes the renderer property which allows you to override token rendering for your whole application.

The example below overrides the default blockquote token rendering by adding a CSS class for custom styling when using Bootstrap CSS:

import { MarkedOptions, MarkedRenderer } from 'ngx-markdown';

// function that returns `MarkedOptions` with renderer override
export function markedOptionsFactory(): MarkedOptions {
  const renderer = new MarkedRenderer();

  renderer.blockquote = (text: string) => {
    return '<blockquote class="blockquote"><p>' + text + '</p></blockquote>';
  };

  return {
    renderer: renderer,
    gfm: true,
    tables: true,
    breaks: false,
    pedantic: false,
    sanitize: false,
    smartLists: true,
    smartypants: false,
  };
}

// using specific option with FactoryProvider
MarkdownModule.forRoot({
  loader: HttpClient,
  markedOptions: {
    provide: MarkedOptions,
    useFactory: markedOptionsFactory,
  },
}),

Other application modules

Use forChild when importing MarkdownModule into other application modules to allow you to use the same parser configuration accross your application.

import { NgModule } from '@angular/core';
+ import { MarkdownModule } from 'ngx-markdown';

import { HomeComponent } from './home.component';

@NgModule({
  imports: [
+   MarkdownModule.forChild(),
  ],
  declarations: [HomeComponent],
})
export class HomeModule { }

Usage

ngx-markdown provides different approaches to help you parse markdown to your application depending of your needs.

💡 As of Angular 6, the template compiler strips whitespace by default. Use ngPreserveWhitespaces directive to preserve whitespaces such as newlines in order for the markdown-formatted content to render as intended.
https://angular.io/api/core/Component#preserveWhitespaces

Component

You can use markdown component to either parse static markdown directly from your html markup, load the content from a remote url using src property or bind a variable to your component using data property. You can get a hook on load complete using load output event property or on loading error using error output event property.

<!-- static markdown -->
<markdown ngPreserveWhitespaces>
  # Markdown
</markdown>

<!-- loaded from remote url -->
<markdown [src]="'path/to/file.md'" (load)="onLoad($event)" (error)="onError($event)"></markdown>

<!-- variable binding -->
<markdown [data]="markdown"></markdown>

Directive

The same way the component works, you can use markdown directive to accomplish the same thing.

<!-- static markdown -->
<div markdown ngPreserveWhitespaces>
  # Markdown
</div>

<!-- loaded from remote url -->
<div markdown [src]="'path/to/file.md'" (load)="onLoad($event)" (error)="onError($event)"></div>

<!-- variable binding -->
<div markdown [data]="markdown"></div>

Pipe

Using markdown pipe to transform markdown to HTML allow you to chain pipe transformations and will update the DOM when value changes.

<!-- chain `language` pipe with `markdown` pipe to convert typescriptMarkdown variable content -->
<div [innerHTML]="typescriptMarkdown | language : 'typescript' | markdown"></div>

Service

You can use MarkdownService to have access to markdown parser and syntax highlight methods.

import { Component, OnInit } from '@angular/core';
import { MarkdownService } from 'ngx-markdown';

@Component({ ... })
export class ExampleComponent implements OnInit() {
  constructor(private markdownService: MarkdownService) { }

  ngOnInit() {
    // outputs: <p>I am using <strong>markdown</strong>.</p>
    console.log(this.markdownService.compile('I am using __markdown__.'));
  }
}

Renderer

Tokens can be render in a custom manner by either...

  • providing the renderer property with the MarkedOptions when importing MarkdownModule.forRoot() into your main application module (see Configuration section)
  • using MarkdownService exposed renderer

Here is an example of overriding the default heading token rendering through MarkdownService by adding an embedded anchor tag like on GitHub:

import { Component, OnInit } from '@angular/core';
import { MarkdownService } from 'ngx-markdown';

@Component({
  selector: 'app-example',
  template: '<markdown># Heading</markdown>',
})
export class ExampleComponent implements OnInit() {
  constructor(private markdownService: MarkdownService) { }

  ngOnInit() {
    this.markdownService.renderer.heading = (text: string, level: number) => {
      const escapedText = text.toLowerCase().replace(/[^\w]+/g, '-');
      return '<h' + level + '>' +
               '<a name="' + escapedText + '" class="anchor" href="#' + escapedText + '">' +
                 '<span class="header-link"></span>' +
               '</a>' + text +
             '</h' + level + '>';
    };
  }
}

This code will output the following HTML:

<h1>
  <a name="heading" class="anchor" href="#heading">
    <span class="header-link"></span>
  </a>
  Heading
</h1>

📘 Follow official marked.renderer documentation for the list of tokens that can be overriden.

Syntax highlight

When using static markdown you are responsible to provide the code block with related language.

<markdown ngPreserveWhitespaces>
+  ```typescript
    const myProp: string = 'value';
+  ```
</markdown>

When using remote url ngx-markdown will use file extension to automatically resolve the code language.

<!-- will use html highlights -->
<markdown [src]="'path/to/file.html'"></markdown>

<!-- will use php highlights -->
<markdown [src]="'path/to/file.php'"></markdown>

When using variable binding you can optionally use language pipe to specify the language of the variable content (default value is markdown when pipe is not used).

<markdown [data]="markdown | language : 'typescript'"></markdown>

Demo application

A demo is available @ https://jfcere.github.io/ngx-markdown and it source code can be found inside the demo directory.

The following commands will clone the repository, install npm dependencies and serve the application @ http://localhost:4200

git clone https://github.com/jfcere/ngx-markdown.git
npm install
ng serve

AoT compilation

Building with AoT is part of the CI and is tested every time a commit occurs so you don't have to worry at all.

Road map

Here is the list of tasks that will be done on this library in a near future ...

  • Add CircleCI integration
  • Publish demo on github pages
  • Add variable binding feature
  • Transpile library to Javascript
  • Make Prism highlight optional
  • Support Prism.js customizing options (line-numbers, line-height, ...)

Contribution

Contributions are always welcome, just make sure that ...

  • Your code style matches with the rest of the project
  • Unit tests pass
  • Linter passes

License

Licensed under MIT.