Den Dribbles

Diagrams With Mermaid

December 18, 2018

This is a small intro into building HTML diagrams on the fly.

I really, really want to be able to visualise some stacks I am building on the go down the track, so I thought this would be a very convenient way to explore that.

Getting started

tl;dr

create-react-app hello-mermaid
cd hello-mermaid
yarn add mermaid debounce

Basics

For this particular example, I decided just to use create-react-app hello-mermaid just to get things up and going.

Once this installs, changed into the folder and either yarn add mermaid or npm install mermaid --save.

In this scenario, I want to also dynamically update the chart, so also add in yarn add debounce or npm install debounce --save as I will use a textarea html element for this which I want to only fire once after being debounced. Check my blog post on debouncing in React for more information.

The code

I decided to start using the the intro learn page for mermaid to get up an going. Following the instructions, I updated my src/App.js file to look like the following:

import React, { Component } from "react"
import "./App.css"
import mermaid from "mermaid"
import debounce from "debounce"

class App extends Component {
  /**
   * Debounce the code first. When the function
   * fires, take the value and attempt to update
   * the Mermaid chart.
   *
   * @memberof App
   */
  handleChange = debounce(
    value => {
      console.log(value)
      var output = document.getElementById("output")
      try {
        mermaid.parse(value)

        output.innerHTML = ""

        mermaid.render("theGraph", value, function(svgCode) {
          console.log(svgCode)
          output.innerHTML = svgCode
        })
      } catch (err) {
        console.error(err)
      }
    },
    600,
    false
  )

  /**
   * Render an initial chart on mount.
   *
   * @memberof App
   */
  componentDidMount() {
    var output = document.getElementById("output")
    mermaid.initialize({ startOnLoad: true })

    var graphDefinition = `graph TB
    a-->b
    b-->a`

    mermaid.render("theGraph", graphDefinition, function(svgCode) {
      output.innerHTML = svgCode
    })
  }

  render() {
    return (
      <div className="App">
        <textarea rows="4" onChange={e => this.handleChange(e.target.value)} />
        <div id="output" />
      </div>
    )
  }
}

export default App

What’s going on here? First of all, I am importing the required packages.

// code omitted for brevity
import mermaid from "mermaid"
import debounce from "debounce"

Secondly, I have updated the render code to give me a div to target with the outputted graph and a text area I can add markdown into:

render() {
    return (
      <div className="App">
        <textarea
          rows="4"
          onChange={(e) => this.handleChange(e.target.value)}
        />
        <div id="output" />
      </div>
    );
  }

Third, I want to initialise the graph with a basic chart:

/**
   * Render an initial chart on mount.
   *
   * @memberof App
   */
  componentDidMount() {
    var output = document.getElementById('output');
    mermaid.initialize({ startOnLoad: true });

    // definition comes from mermaid
    var graphDefinition = `graph TB
    a-->b
    b-->a`;

    mermaid.render('theGraph', graphDefinition, function(svgCode) {
      output.innerHTML = svgCode;
    });
  }

Finally, I add the handleChange function to attempt an update to the graph.

/**
 * Debounce the code first. When the function
 * fires, take the value and attempt to update
 * the Mermaid chart.
 *
 * @memberof App
 */
handleChange = debounce(
  value => {
    console.log(value)
    var output = document.getElementById("output")
    try {
      // use the mermaid parse first to
      // ensure code is parsable. If not,
      // throw an error, handle it gracefully
      // and do nothing.
      mermaid.parse(value)

      output.innerHTML = ""

      mermaid.render("theGraph", value, function(svgCode) {
        console.log(svgCode)
        output.innerHTML = svgCode
      })
    } catch (err) {
      console.error(err)
    }
  },
  600,
  false
)

When we run yarn start on the terminal and the web page opens up, we get the following image:

Initial app

Great! Now thanks to our handleChange function and graceful handling, we can also dynamically update the chart on the fly.

I’ve added a few examples from the web that you can now copy and paste into our text box to see how it works!

graph LR
    A[Hard edge] -->|Link text| B(Round edge)
    B --> C{Decision}
    C -->|One| D[Result one]
    C -->|Two| E[Result two]

Graph

sequenceDiagram
    Alice->>+John: Hello John, how are you?
    Alice->>+John: John, can you hear me?
    John-->>-Alice: Hi Alice, I can hear you!
    John-->>-Alice: I feel great!

Sequence diagram

gantt
       dateFormat  YYYY-MM-DD
       title Adding GANTT diagram functionality to mermaid

       section A section
       Completed task            :done,    des1, 2014-01-06,2014-01-08
       Active task               :active,  des2, 2014-01-09, 3d
       Future task               :         des3, after des2, 5d
       Future task2              :         des4, after des3, 5d

       section Critical tasks
       Completed task in the critical line :crit, done, 2014-01-06,24h
       Implement parser and jison          :crit, done, after des1, 2d
       Create tests for parser             :crit, active, 3d
       Future task in critical line        :crit, 5d
       Create tests for renderer           :2d
       Add to mermaid                      :1d

       section Documentation
       Describe gantt syntax               :active, a1, after des1, 3d
       Add gantt diagram to demo page      :after a1  , 20h
       Add another diagram to demo page    :doc1, after a1  , 48h

       section Last section
       Describe gantt syntax               :after doc1, 3d
       Add gantt diagram to demo page      :20h
       Add another diagram to demo page    :48h

Gantt

Next steps

Very cool! Now we can easily start creating some cool dynamic flows. What next? Be creative! I am planning to parse the markdown or html from the outputs and use it to help generate important reports or pseudocode to help build out some infrastructure or database schemas.

You can see the final code on the repo here.

Also, checkout their docs to see what else you can do!

Depth is a series that goes into more detail for projects than it’s friendly counterpart series “Hello”.


A personal blog on all things of interest. Written by Dennis O'Keeffe, Follow me on Twitter