Section:

Side-by-Side Showcase Demo Code Sample

Requirements
View Demo
Web SDK

Quickly view and compare PDFs, Office documents, and images with a side-by-side layout. Keep both documents in sync as you scroll and zoom for a seamless comparison experience.

This demo allows you to:

  • Upload and choose your own documents.
  • View two files side-by-side.
  • Toggle synchronized scrolling and zooming between documents.

Implementation steps

To add Side-by-Side viewing capability with WebViewer:
Step 1: Get started with WebViewer in your preferred web stack.
Step 2: Add the ES6 JavaScript sample code provided in this guide.

Once you generate your license key, it will automatically be included in your sample code below.

License Key

1// ES6 Compliant Syntax
2// GitHub Copilot, Claude Sonnet 4 (Preview), October 16, 2025
3// File: showcase-demos/side-by-side/index.js
4import WebViewer from '@pdftron/webviewer';
5
6// Global variables to track state.
7const defaultDoc1 = 'https://apryse.s3.us-west-1.amazonaws.com/public/files/samples/demo-annotated.pdf';
8const defaultDoc2 = 'https://apryse.s3.us-west-1.amazonaws.com/public/files/samples/WebviewerDemoDoc.pdf';
9let syncScroll = false;
10let isUpdatingSync = false; // Guard flag to prevent circular calls.
11let file1 = null;
12let file2 = null;
13let title1 = '';
14let title2 = '';
15let canStartComparing = false;
16
17// Store references for cleanup.
18let documentViewer1 = null;
19let documentViewer2 = null;
20let multiViewerReadyHandler = null;
21let documentLoadedHandler1 = null;
22let documentLoadedHandler2 = null;
23
24// Function to initialize and load the Redaction Tool.
25function initializeWebViewer() {
26
27  const element = document.getElementById('viewer');
28  if (!element) {
29    console.error('Viewer div not found.');
30    return;
31  }
32
33  WebViewer({
34    path: '/lib',
35    licenseKey: 'YOUR_LICENSE_KEY',
36  }, element).then(instance => {    
37    // Get Core and UI from the instance.
38    const { Core, UI } = instance;
39
40    createUIElements();
41    UI.enableElements(['contentEditButton']);
42    UI.disableElements(['comparisonToggleButton']);
43    UI.enableFeatures([UI.Feature.MultiViewerMode]);
44    UI.enterMultiViewerMode();
45    // Create the multi-viewer ready handler.
46    multiViewerReadyHandler = () => {
47      // Now, both document viewers are available.
48      documentViewer1 = Core.getDocumentViewers()[0];
49      documentViewer2 = Core.getDocumentViewers()[1];
50
51      // Create document loaded handlers.
52      documentLoadedHandler1 = () => {
53        file1 = documentViewer1.getDocument();
54      };
55
56      documentLoadedHandler2 = () => {
57        file2 = documentViewer2.getDocument();
58      };
59
60      // Add document loaded event listeners.
61      documentViewer1.addEventListener('documentLoaded', documentLoadedHandler1);
62      documentViewer2.addEventListener('documentLoaded', documentLoadedHandler2);
63
64      // Load default documents into both viewers.
65      documentViewer1?.loadDocument(defaultDoc1);
66      documentViewer2?.loadDocument(defaultDoc2);
67      
68      // Add event listeners to sync scroll & zoom button in both viewers.
69      addSyncListener(documentViewer1, UI, syncScroll);
70      addSyncListener(documentViewer2, UI, syncScroll);
71    };
72
73    // Set up multi-viewer ready event.
74    UI.addEventListener(UI.Events.MULTI_VIEWER_READY, multiViewerReadyHandler);
75
76  }).catch(error => {
77    console.error('Error initializing WebViewer:', error);
78  });
79}
80
81// Add event listener to sync scroll & zoom button in multi-viewer mode.
82function addSyncListener(
83  documentViewer,
84  UI,
85  syncScroll
86) {
87  documentViewer
88    ?.getViewerElement()
89    ?.closest('.CompareContainer')
90    // The first button is the "Start Sync" button.
91    ?.querySelector('.control-buttons button')
92    ?.addEventListener('click', () => {
93      setTimeout(() => {
94        syncScroll = UI.isMultiViewerSyncing();
95        setSyncScroll(syncScroll);
96        isUpdatingSync = true;
97        UIElements.updateSyncToggleUIOnly(syncScroll);
98      }, 0);
99    });
100};
101
102// Function to sync up document viewers to scroll and zoom together.
103function setSyncScroll(value) {
104  syncScroll = value;
105  toggleSyncScrollZoom(syncScroll);
106}
107
108// Function to enable/disable sync scroll & zoom.
109function toggleSyncScrollZoom(enable) {
110  if (enable) {
111    window.WebViewer.getInstance().UI.enableMultiViewerSync();
112    console.log('Sync scroll & zoom enabled');
113    syncScroll = true;
114  } else {
115    window.WebViewer.getInstance().UI.disableMultiViewerSync();
116    console.log('Sync scroll & zoom disabled');
117    syncScroll = false;  
118  }  
119}
120
121// Expose file variables and functions to the global scope for UI interaction.
122window.toggleSyncScrollZoom = toggleSyncScrollZoom;
123window.isUpdatingSync = isUpdatingSync;
124window.file1 = file1;
125window.file2 = file2;
126window.title1 = title1;
127window.title2 = title2;
128window.canStartComparing = canStartComparing;
129
130// UI Elements
131// Function to create and initialize UI elements.
132function createUIElements() {
133  // Create a container for all controls (label, dropdown, and buttons).
134  // Dynamically load ui-elements.js if not already loaded.
135  if (!window.SidePanel) {
136    const script = document.createElement('script');
137    script.src = '/showcase-demos/side-by-side/ui-elements.js';
138    script.onload = () => {
139      UIElements.init('viewer');
140    };
141    document.head.appendChild(script);
142  }
143}
144
145// Initialize the WebViewer.
146initializeWebViewer();
147

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