# Using GoJS with React

Examples of most of the topics discussed on this page can be found in the gojs-react-basic project, which serves as a simple starter project.

If you are new to GoJS, it may be helpful to first visit the Getting Started Tutorial.

The easiest way to get a component set up for a GoJS Diagram is to use the gojs-react package, which exports React Components for GoJS Diagrams, Palettes, and Overviews. The gojs-react-basic project demonstrates how to use these components. More information about the package, including the various props it takes, can be found on the Github or NPM pages. Our examples will be using a GraphLinksModel, but any model can be used.

## Quick start with an existing React application

#### Installation

Start by installing GoJS and gojs-react: `npm install gojs gojs-react`.

#### Diagram styling

Next, set up a CSS class for the GoJS diagram's div:

      /* App.css */
      .diagram-component {
        width: 400px;
        height: 400px;
        border: solid 1px black;
        background-color: white;
      }

#### Rendering the component

Finally, add an initDiagram function and a model change handler function, and add the ReactDiagram component inside your render method.

      // App.js
      import React from 'react';

      import * as go from 'gojs';
      import { ReactDiagram } from 'gojs-react';

      import './App.css';  // contains .diagram-component CSS

      // ...

      /**
       * This function is responsible for setting up the diagram's initial properties and any templates.
       */
      function initDiagram() {
        const $ = go.GraphObject.make;
        const diagram =
          $(go.Diagram,
            {
              'undoManager.isEnabled': true,  // enable undo & redo
              'clickCreatingTool.archetypeNodeData': { text: 'new node', color: 'lightblue' },
              model: $(go.GraphLinksModel,
                {
                  linkKeyProperty: 'key'  // IMPORTANT! must be defined for merges and data sync when using GraphLinksModel
                })
            });

        // define a simple Node template
        diagram.nodeTemplate =
          $(go.Node, 'Auto',  // the Shape will go around the TextBlock
            new go.Binding('location', 'loc', go.Point.parse).makeTwoWay(go.Point.stringify),
            $(go.Shape, 'RoundedRectangle',
              { name: 'SHAPE', fill: 'white', strokeWidth: 0 },
              // Shape.fill is bound to Node.data.color
              new go.Binding('fill', 'color')),
            $(go.TextBlock,
              { margin: 8, editable: true },  // some room around the text
              new go.Binding('text').makeTwoWay()
            )
          );

        return diagram;
      }

      /**
       * This function handles any changes to the GoJS model.
       * It is here that you would make any updates to your React state, which is dicussed below.
       */
      function handleModelChange(changes) {
        alert('GoJS model changed!');
      }

      // render function...
      function App() {
        return (
          <div>
            ...
            <ReactDiagram
              initDiagram={initDiagram}
              divClassName='diagram-component'
              nodeDataArray={[
                { key: 0, text: 'Alpha', color: 'lightblue', loc: '0 0' },
                { key: 1, text: 'Beta', color: 'orange', loc: '150 0' },
                { key: 2, text: 'Gamma', color: 'lightgreen', loc: '0 150' },
                { key: 3, text: 'Delta', color: 'pink', loc: '150 150' }
              ]}
              linkDataArray={[
                { key: -1, from: 0, to: 1 },
                { key: -2, from: 0, to: 2 },
                { key: -3, from: 1, to: 1 },
                { key: -4, from: 2, to: 3 },
                { key: -5, from: 3, to: 0 }
              ]}
              onModelChange={handleModelChange}
            />
            ...
          </div>
        );
      }

That's it! You should now have a GoJS diagram rendering within your React application. Try editing the text of a node or deleting a node, and you'll see an alert on the page.

## Usage in a stateful React app

Typically the data being passed to the ReactDiagram component will be used elsewhere in your app and will exist in React state. For example, you may have some kind of inspector that can be used to modify node properties, and therefore the state should be lifted up and held by a parent component of both the diagram and the inspector.

A basic setup can be seen in the gojs-react-basic project, but we'll describe some of the methodology here.

#### Creating a wrapper component

When handling state, it is often useful to write a wrapper component around the gojs-react components to pass the necessary props along and keep GoJS initialization out of the main app. There are a few things that should be set up in the wrapper component:

- a set of props coming in from the parent component which holds state and handlers
- a ref to the ReactDiagram component so getDiagram() can be used
- componentDidMount and componentWillUnmount methods to add/remove app-specific diagram listeners
- an initDiagram method to be passed to the ReactDiagram component

      import * as go from 'gojs';
      import { ReactDiagram } from 'gojs-react';
      import * as React from 'react';

      // props passed in from a parent component holding state, some of which will be passed to ReactDiagram
      interface WrapperProps {
        nodeDataArray: Array<go.ObjectData>;
        linkDataArray: Array<go.ObjectData>;
        modelData: go.ObjectData;
        skipsDiagramUpdate: boolean;
        onDiagramEvent: (e: go.DiagramEvent) => void;
        onModelChange: (e: go.IncrementalData) => void;
      }

      export class DiagramWrapper extends React.Component<WrapperProps, {}> {
        /**
         * Ref to keep a reference to the component, which provides access to the GoJS diagram via getDiagram().
         */
        private diagramRef: React.RefObject<ReactDiagram>;

        constructor(props: WrapperProps) {
          super(props);
          this.diagramRef = React.createRef();
        }

        /**
         * Get the diagram reference and add any desired diagram listeners.
         * Typically the same function will be used for each listener,
         * with the function using a switch statement to handle the events.
         * This is only necessary when you want to define additional app-specific diagram listeners.
         */
        public componentDidMount() {
          if (!this.diagramRef.current) return;
          const diagram = this.diagramRef.current.getDiagram();
          if (diagram instanceof go.Diagram) {
            diagram.addDiagramListener('ChangedSelection', this.props.onDiagramEvent);
          }
        }

        /**
         * Get the diagram reference and remove listeners that were added during mounting.
         * This is only necessary when you have defined additional app-specific diagram listeners.
         */
        public componentWillUnmount() {
          if (!this.diagramRef.current) return;
          const diagram = this.diagramRef.current.getDiagram();
          if (diagram instanceof go.Diagram) {
            diagram.removeDiagramListener('ChangedSelection', this.props.onDiagramEvent);
          }
        }

        /**
         * Diagram initialization method, which is passed to the ReactDiagram component.
         * This method is responsible for making the diagram and initializing the model, any templates,
         * and maybe doing other initialization tasks like customizing tools.
         * The model's data should not be set here, as the ReactDiagram component handles that via the other props.
         */
        private initDiagram(): go.Diagram {
          const $ = go.GraphObject.make;
          const diagram =
            $(go.Diagram,
              {
                'undoManager.isEnabled': true,  // enable undo & redo
                'clickCreatingTool.archetypeNodeData': { text: 'new node', color: 'lightblue' },
                model: $(go.GraphLinksModel,
                  {
                    linkKeyProperty: 'key',  // IMPORTANT! must be defined for merges and data sync when using GraphLinksModel
                    // positive keys for nodes
                    makeUniqueKeyFunction: (m: go.Model, data: any) => {
                      let k = data.key || 1;
                      while (m.findNodeDataForKey(k)) k++;
                      data.key = k;
                      return k;
                    },
                    // negative keys for links
                    makeUniqueLinkKeyFunction: (m: go.GraphLinksModel, data: any) => {
                      let k = data.key || -1;
                      while (m.findLinkDataForKey(k)) k--;
                      data.key = k;
                      return k;
                    }
                  })
              });

          // define a simple Node template
          diagram.nodeTemplate =
            $(go.Node, 'Auto',  // the Shape will go around the TextBlock
              new go.Binding('location', 'loc', go.Point.parse).makeTwoWay(go.Point.stringify),
              $(go.Shape, 'RoundedRectangle',
                {
                  name: 'SHAPE', fill: 'white', strokeWidth: 0,
                  // set the port properties:
                  portId: '', fromLinkable: true, toLinkable: true, cursor: 'pointer'
                },
                // Shape.fill is bound to Node.data.color
                new go.Binding('fill', 'color')),
              $(go.TextBlock,
                { margin: 8, editable: true, font: '400 .875rem Roboto, sans-serif' },  // some room around the text
                new go.Binding('text').makeTwoWay()
              )
            );

          // relinking depends on modelData
          diagram.linkTemplate =
            $(go.Link,
              new go.Binding('relinkableFrom', 'canRelink').ofModel(),
              new go.Binding('relinkableTo', 'canRelink').ofModel(),
              $(go.Shape),
              $(go.Shape, { toArrow: 'Standard' })
            );

          return diagram;
        }

        public render() {
          return (
            <ReactDiagram
              ref={this.diagramRef}
              divClassName='diagram-component'
              initDiagram={this.initDiagram}
              nodeDataArray={this.props.nodeDataArray}
              linkDataArray={this.props.linkDataArray}
              modelData={this.props.modelData}
              onModelChange={this.props.onModelChange}
              skipsDiagramUpdate={this.props.skipsDiagramUpdate}
            />
          );
        }
      }

#### Using the wrapper component within the app

The application should set up a few things to be passed to the wrapper described above:

- state containing a nodeDataArray, linkDataArray, modelData object, and skipsDiagramUpdate flag
- a handleDiagramEvent method for any app-specific DiagramEvents, such as 'ChangedSelection'
- a handleModelChange method for updating state based on updates from the GoJS model

      import * as go from 'gojs';
      import * as React from 'react';

      import { DiagramWrapper } from './components/Diagram';

      interface AppState {
        // ...
        nodeDataArray: Array<go.ObjectData>;
        linkDataArray: Array<go.ObjectData>;
        modelData: go.ObjectData;
        selectedKey: number | null;
        skipsDiagramUpdate: boolean;
      }

      class App extends React.Component<{}, AppState> {
        constructor(props: object) {
          super(props);
          this.state = {
            // ...
            nodeDataArray: [
              { key: 0, text: 'Alpha', color: 'lightblue', loc: '0 0' },
              { key: 1, text: 'Beta', color: 'orange', loc: '150 0' },
              { key: 2, text: 'Gamma', color: 'lightgreen', loc: '0 150' },
              { key: 3, text: 'Delta', color: 'pink', loc: '150 150' }
            ],
            linkDataArray: [
              { key: -1, from: 0, to: 1 },
              { key: -2, from: 0, to: 2 },
              { key: -3, from: 1, to: 1 },
              { key: -4, from: 2, to: 3 },
              { key: -5, from: 3, to: 0 }
            ],
            modelData: {
              canRelink: true
            },
            selectedKey: null,
            skipsDiagramUpdate: false
          };
          // bind handler methods
          this.handleDiagramEvent = this.handleDiagramEvent.bind(this);
          this.handleModelChange = this.handleModelChange.bind(this);
          this.handleRelinkChange = this.handleRelinkChange.bind(this);
        }

        /**
         * Handle any app-specific DiagramEvents, in this case just selection changes.
         * On ChangedSelection, find the corresponding data and set the selectedKey state.
         *
         * This is not required, and is only needed when handling DiagramEvents from the GoJS diagram.
         * @param e a GoJS DiagramEvent
         */
        public handleDiagramEvent(e: go.DiagramEvent) {
          const name = e.name;
          switch (name) {
            case 'ChangedSelection': {
              const sel = e.subject.first();
              if (sel) {
                this.setState({ selectedKey: sel.key });
              } else {
                this.setState({ selectedKey: null });
              }
              break;
            }
            default: break;
          }
        }

        /**
         * Handle GoJS model changes, which output an object of data changes via Model.toIncrementalData.
         * This method should iterates over those changes and update state to keep in sync with the GoJS model.
         * This can be done via setState in React or another preferred state management method.
         * @param obj a JSON-formatted string
         */
        public handleModelChange(obj: go.IncrementalData) {
          const insertedNodeKeys = obj.insertedNodeKeys;
          const modifiedNodeData = obj.modifiedNodeData;
          const removedNodeKeys = obj.removedNodeKeys;
          const insertedLinkKeys = obj.insertedLinkKeys;
          const modifiedLinkData = obj.modifiedLinkData;
          const removedLinkKeys = obj.removedLinkKeys;
          const modifiedModelData = obj.modelData;

          console.log(obj);

          // see gojs-react-basic for an example model change handler
          // when setting state, be sure to set skipsDiagramUpdate: true since GoJS already has this update
        }

        /**
         * Handle changes to the checkbox on whether to allow relinking.
         * @param e a change event from the checkbox
         */
        public handleRelinkChange(e: any) {
          const target = e.target;
          const value = target.checked;
          this.setState({ modelData: { canRelink: value }, skipsDiagramUpdate: false });
        }

        public render() {
          let selKey;
          if (this.state.selectedKey !== null) {
            selKey = <p>Selected key: {this.state.selectedKey}</p>;
          }

          return (
            <div>
              <DiagramWrapper
                nodeDataArray={this.state.nodeDataArray}
                linkDataArray={this.state.linkDataArray}
                modelData={this.state.modelData}
                skipsDiagramUpdate={this.state.skipsDiagramUpdate}
                onDiagramEvent={this.handleDiagramEvent}
                onModelChange={this.handleModelChange}
              />
              <label>
                Allow Relinking?
                <input
                  type='checkbox'
                  id='relink'
                  checked={this.state.modelData.canRelink}
                  onChange={this.handleRelinkChange} />
              </label>
              {selKey}
            </div>
          );
        }
      }

These are the basics for setting up GoJS within a React application. See gojs-react-basic for a working example and the gojs-react Github page for further explanation of various props passed to the components.