GoJS Is Undefined In Second Aura Component When Loaded Via Ltng:require

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When developing Salesforce Aura Components that rely on external JavaScript libraries like GoJS, encountering issues where the library appears undefined in certain components can be a significant hurdle. This article delves into the common causes behind the GoJS is undefined error in a multi-component Aura application, particularly when loading GoJS via <ltng:require> tag, and provides detailed solutions to ensure your components function seamlessly.

Understanding the Challenge: JavaScript Libraries in Aura Components

The Aura framework provides a mechanism to incorporate third-party JavaScript libraries into your components using the <ltng:require> tag. This tag is designed to load scripts and style sheets, making them available for your component's use. However, the asynchronous nature of script loading and the component lifecycle in Aura can sometimes lead to unexpected behavior, especially when multiple components depend on the same library.

The primary challenge arises when two or more components attempt to load the same JavaScript library. Due to the asynchronous loading, one component might try to access the library before it has been fully loaded by another component. This results in the dreaded GoJS is undefined error, halting the execution of your component's JavaScript code.

Common Causes of the GoJS is undefined Error

To effectively troubleshoot this issue, it's crucial to understand the common scenarios that trigger the GoJS is undefined error in a multi-component Aura setup:

  1. Asynchronous Loading Race Condition: This is the most frequent culprit. When two components, say ComponentA and ComponentB, both use <ltng:require> to load GoJS, the order in which these scripts are loaded and executed is not guaranteed. If ComponentB tries to use GoJS before ComponentA's <ltng:require> has completed loading and initializing the library, it will encounter the undefined error.

  2. Incorrect Scope and Namespace Conflicts: JavaScript libraries often attach themselves to the global scope (e.g., the window object in browsers). If GoJS is loaded within a specific scope or if there are naming conflicts with other libraries, Aura Components might not be able to access the GoJS object correctly. This can happen if GoJS library's internal structure or if the way it exposes its functionality doesn't align with Aura's expectations.

  3. Component Lifecycle Issues: Aura components have a well-defined lifecycle, including initialization, rendering, and unrendering phases. If a component attempts to use GoJS during a phase where the library hasn't been loaded yet (e.g., in the init handler before <ltng:require> has finished), the error will occur.

  4. Caching and Browser Behavior: Browsers aggressively cache JavaScript files to improve performance. In some cases, an outdated version of GoJS might be cached, or the browser might not correctly handle the loading of the script across different components. This can lead to inconsistent behavior and the undefined error.

Step-by-Step Solutions to Resolve GoJS is undefined

Now that we've identified the common causes, let's explore practical solutions to fix the GoJS is undefined error in your Aura Components:

1. Centralized Script Loading

The most robust solution is to centralize the loading of GoJS in a single location. This ensures that the library is loaded only once and is available to all components that need it. Here's how to implement this approach:

  • Create a Master Component: Designate one component as the "master" component responsible for loading GoJS. This component should include the <ltng:require> tag for GoJS.

    <!-- MasterComponent.cmp -->
<aura:component>
    <ltng:require scripts="{!$Resource.goJS}" afterScriptsLoaded="{!c.scriptsLoaded}" />
    <!-- Other component logic -->
</aura:component>

    // MasterComponentController.js
({  scriptsLoaded : function(component, event, helper) {
        // GoJS is now loaded and available
        // You can perform initialization tasks here
        console.log('GoJS loaded successfully');
    }
})

  • Embed the Master Component: Include the MasterComponent in the topmost component in your application or in a common parent component that all other components share. This ensures that GoJS is loaded before any other component tries to use it.

    <!-- ParentComponent.cmp -->
<aura:component>
    <c:MasterComponent />
    <!-- Other components -->
</aura:component>

  • Event-Driven Communication: Use application events to notify other components when GoJS has been loaded. The MasterComponent can fire an application event in its scriptsLoaded handler, and other components can listen for this event to know when GoJS is ready.

    <!-- MasterComponentController.js -->
({  scriptsLoaded : function(component, event, helper) {
        // GoJS is now loaded and available
        // Fire an application event
        var appEvent = $A.get("e.c:GoJSLoadedEvent");
        appEvent.fire();
        console.log('GoJS loaded successfully, event fired');
    }
})

    <!-- GoJSLoadedEvent.evt -->
<aura:event type="APPLICATION" description="Event fired when GoJS is loaded."/>

    <!-- ComponentB.cmp -->
<aura:component implements="forceCommunity:availableForAllPageTypes" access="global">
<aura:handler event="c:GoJSLoadedEvent" action="{!c.handleGoJSLoaded}"/>
<!-- Other component logic -->
</aura:component>

    // ComponentBController.js
({  handleGoJSLoaded : function(component, event, helper) {
    // GoJS is now available, you can use it here
    console.log('GoJS is ready in ComponentB');
    }
})

This centralized loading approach eliminates the race condition and ensures that GoJS is loaded and initialized only once, preventing the undefined error.

2. Promises and Asynchronous Handling

If you cannot centralize the script loading, you can use Promises to manage the asynchronous loading of GoJS within each component. This ensures that the component only attempts to use GoJS after it has been successfully loaded.

  • Wrap <ltng:require> in a Promise: Create a helper function that returns a Promise that resolves when GoJS is loaded. If the same component instances require a similar function, store this function into a helper.js file
// ComponentAHelper.js
({  loadGoJS: function(component) {
        return new Promise(function(resolve, reject) {
            $Lightning.use("ltng:require", function() {
                $Lightning.require("{!$Resource.goJS}", function() {
                    resolve();
                });
            });
        });
    }
})
  • Use the Promise Before Accessing GoJS: In your component's controller, use the Promise to ensure that GoJS is loaded before you attempt to use it.
// ComponentAController.js
({  doInit: function(component, event, helper) {
        helper.loadGoJS(component)
            .then($A.getCallback(function() {
                // GoJS is now loaded, you can use it here
                console.log('GoJS is ready in ComponentA');
                // Initialize GoJS diagrams or perform other tasks
            }))
            .catch(function(error) {
                // Handle the error if GoJS fails to load
                console.error('Error loading GoJS:', error);
            });
    }
})

This approach provides a more controlled way to handle the asynchronous loading of GoJS and prevents the undefined error by ensuring that the library is available before it's used.

3. Static Resources and Caching

Ensure that your GoJS library is uploaded as a static resource in Salesforce. This is the recommended way to include external JavaScript libraries in Aura Components. Additionally, be mindful of browser caching.

  • Version Your Static Resource: When you update the GoJS library, upload it as a new static resource with a different name or version number. This forces the browser to download the latest version and prevents caching issues.

  • Clear Browser Cache: If you suspect caching is causing the issue, clear your browser's cache and try again. This ensures that you're loading the most recent version of the library.

4. Debugging Techniques

When troubleshooting the GoJS is undefined error, these debugging techniques can provide valuable insights:

  • Console Logging: Use console.log() statements to check when GoJS is being loaded and when components are trying to access it. This can help you identify the timing issues.

  • Aura Debugger: The Aura Debugger in the Salesforce Developer Console provides detailed information about component initialization, event handling, and script loading. Use it to step through your code and identify the exact point where the error occurs.

  • Browser Developer Tools: Use your browser's developer tools (e.g., Chrome DevTools) to inspect the network requests and ensure that the GoJS script is being loaded successfully. Check the console for any JavaScript errors.

Best Practices for Using JavaScript Libraries in Aura Components

To avoid issues with JavaScript libraries in Aura Components, follow these best practices:

  • Load Libraries Once: Centralize the loading of libraries whenever possible to prevent race conditions and improve performance.
  • Use Promises for Asynchronous Loading: If you cannot centralize loading, use Promises to manage the asynchronous loading of libraries within each component.
  • Handle Errors Gracefully: Implement error handling to catch and log any errors that occur during script loading.
  • Version Static Resources: Use versioning for static resources to manage updates and prevent caching issues.
  • Test Thoroughly: Test your components in different browsers and environments to ensure that the libraries are loaded and working correctly.

Conclusion

The GoJS is undefined error in a multi-component Aura application can be frustrating, but by understanding the common causes and implementing the solutions outlined in this article, you can effectively resolve the issue. Centralized script loading, Promises, careful caching management, and robust debugging techniques are your allies in ensuring that your Aura Components seamlessly integrate with external JavaScript libraries like GoJS. By following best practices and paying attention to the component lifecycle and asynchronous loading, you can build robust and reliable Aura applications that leverage the power of third-party libraries.