ngx-markdown

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

• Demo available @ https://jfcere.github.io/ngx-markdown
• Plunker available @ https://plnkr.co/edit/y5LPj7?p=preview
• StackBlitz available @ https://stackblitz.com/edit/ngx-markdown

Table of contents

• Installation
• Configuration
• Usage
• Renderer
• Syntax highlight
• Demo application
• AoT compilation
• Road map
• Contribution

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
]

Line Numbers plugin

To use the line numbers plugin that shows line numbers in code blocks, in addition to Prism.js configuration files, you will need to include the following files from prismjs/plugins/line-numbers directory to your application:

• CSS styling for line numbers - prism-line-numbers.css
• line numbers plugin script - prism-line-numbers.js

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

"styles": [
  "src/styles.css",
  "node_modules/prismjs/themes/prism-okaidia.css",
+ "node_modules/prismjs/plugins/line-numbers/prism-line-numbers.css"
],
"scripts": [
  "node_modules/prismjs/prism.js",
  "node_modules/prismjs/components/prism-csharp.min.js",
  "node_modules/prismjs/components/prism-css.min.js",
+ "node_modules/prismjs/plugins/line-numbers/prism-line-numbers.js"
]

Using markdown component and/or directive, you will be able to use the lineNumbers property to activate the plugin. The property can be used in combination with either data for variable binding, src for remote content or using transclusion for static markdown.

Additionally, you can use start input property to specify the offset number for the first display line.

<markdown [src]="path/to/file.js" lineNumbers [start]="5"></markdown>

Line Highlight plugin

To use the line highlight plugin that highlights specific lines and/or line ranges in code blocks, in addition to Prism.js configuration files, you will need to include the following files from prismjs/plugins/line-highlight directory to your application:

• CSS styling for line highlight - prism-line-highlight.css
• line highlight plugin script - prism-line-highlight.js

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

"styles": [
  "src/styles.css",
  "node_modules/prismjs/themes/prism-okaidia.css",
+ "node_modules/prismjs/plugins/line-highlight/prism-line-highlight.css"
],
"scripts": [
  "node_modules/prismjs/prism.js",
  "node_modules/prismjs/components/prism-csharp.min.js",
  "node_modules/prismjs/components/prism-css.min.js",
+ "node_modules/prismjs/plugins/line-highlight/prism-line-highlight.js"
]

Using markdown component and/or directive, you will be able to use the lineHighlight property to activate the plugin. The property can be used in combination with either data for variable binding, src for remote content or using transclusion for static markdown.

Use line input property to specify the line(s) to highlight and optionally there is a lineOffset property to specify the starting line of code your snippet represents.

<markdown [src]="path/to/file.js" lineHighlight [line]="'6, 10-16'" [lineOffset]="5"></markdown>

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

Optionally, 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 across 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 on 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 rendered 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 the 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 its 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 the 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.