Fix Chart.js MwoWUuIu.js 404 Error: Complete Guide

Chart.js references a non-existent file ‘MwoWUuIu.js’ due to a source map configuration issue or a build artifact that gets incorrectly included during the library’s bundling process. This typically occurs when the development version of Chart.js is used instead of the production version, or when there are issues with how the library is being imported in your project. The 404 error happens because browsers attempt to load the source map file referenced at the top of the Chart.js file, but this file doesn’t exist in the distribution.

Contents

• Understanding the MwoWUuIu.js Reference Issue
• Common Causes of 404 Errors with Chart.js
• Solutions to Fix the MwoWUuIu.js 404 Error
• Best Practices for Chart.js Integration
• When to Report Issues to Chart.js Maintainers

Understanding the MwoWUuIu.js Reference Issue

The MwoWUuIu.js file reference typically appears at the top of Chart.js files as a source map declaration. This is a common pattern in JavaScript bundling where development tools generate source maps to help developers debug minified code by mapping it back to the original source files.

When you see a line like:

//# sourceMappingURL=../_/MwoWUuIu.js

This tells the browser’s developer tools where to find the source map file that maps the minified code back to its original source. However, when this file doesn’t exist or isn’t properly included in the distribution package, you’ll see a 404 error in the browser console.

According to Microsoft’s documentation on source maps, source maps are essential for debugging but can cause 404 errors when not properly configured or when using development builds in production environments.

Common Causes of 404 Errors with Chart.js

1. Using Development Builds in Production

The most common cause is using a development build of Chart.js in a production environment. Development builds often include source map references that aren’t needed in production and can cause 404 errors.

As noted in the Stack Overflow discussion about Chart.js source map issues, “It turns out that chart.js just updated to v4.0.1 two days ago, and includes some breaking changes. So I pinned the version of chart.js that my site uses” source.

2. Incorrect Import Configuration

Many developers encounter 404 errors due to incorrect import configurations, especially in frameworks like Angular and Salesforce Lightning Web Components.

For example, in Salesforce Lightning Web Components, the issue often stems from incorrect resource loading:

Promise.all([
    loadScript(this, ChartsJS + '/Chart.js')
]).then(() => {
    // Chart.js loaded successfully
}).catch(error => {
    console.log("Cant load CHARTJS");
});

According to the Salesforce StackExchange answer, applying the correct resource loading configuration resolves the 404 error.

3. CDN and Hosting Issues

When using Chart.js from CDNs like jsdelivr, there can be issues with how the library files are served or cached. The GitHub discussion explains that “jsdelivr automagically minifies the source, when its name does not contain .min (this is a guess) and does not generate sourcemap for it.”

4. Version Conflicts

Having multiple versions of Chart.js or conflicting library versions can also cause 404 errors. As one Stack Overflow answer points out: “Also try not to use duplicate versions of a lib, you have version 2.8 and 2.9.4 of chartjs as script tags included”

Solutions to Fix the MwoWUuIu.js 404 Error

1. Use the Production Version

The simplest solution is to use the minified production version of Chart.js instead of the development version. The production version doesn’t include source map references.

<!-- Use this instead of development version -->
<script src="https://cdn.jsdelivr.net/npm/chart.js@4.5.1/dist/chart.min.js"></script>

According to the Chart.js documentation, “Chart.js is tree-shakeable, so it is necessary to import and register the controllers, elements, scales and plugins you are going to use.”

2. Disable Source Maps in Browser DevTools

If you don’t need source maps for debugging, you can disable them in your browser’s developer tools:

• In Chrome: Go to Settings > More tools > Developer tools > Preferences > Sources and disable “Enable JavaScript source maps”
• In Firefox: Go to Settings > Developer > Debugger and disable “Show original sources”

3. Proper Framework Integration

For different frameworks, there are specific solutions:

Angular/ng2-charts

For Angular projects, ensure proper configuration in your systemjs.config.js:

'ng2-charts': 'npm:ng2-charts/bundles/ng2-charts.umd.min.js'

As noted in the Stack Overflow answer, this configuration works perfectly for Angular 4.3.4 with ng2-charts 1.6.0.

Salesforce Lightning Web Components

Use the correct platform resource loading:

import { loadStyle, loadScript } from 'lightning/platformResourceLoader';
import ChartsJS from '@salesforce/resourceUrl/ChartsJS';

getAddressCharts(e) {
    Promise.all([
        loadScript(this, ChartsJS + '/Chart.js')
    ]).then(() => {
        // Chart.js loaded successfully
    }).catch(error => {
        console.log("Cant load CHARTJS");
    });
}

4. Local Installation

If CDN issues persist, consider installing Chart.js locally:

npm install chart.js@4.5.1

Then import it in your project:

import { Chart } from 'chart.js';

Best Practices for Chart.js Integration

1. Version Pinning

Pin to specific versions to avoid breaking changes:

<script src="https://cdn.jsdelivr.net/npm/chart.js@4.5.1/dist/chart.min.js"></script>

2. Use Import Maps for Modern Projects

For modern JavaScript projects, use import maps:

<script type="importmap">
{
    "imports": {
        "chart.js": "https://cdn.skypack.dev/chart.js"
    }
}
</script>

This approach, as shown in the 12 Days of Web documentation, provides better dependency management.

3. Module-Based Import

For build tools like Webpack or Vite, use ES modules:

import { Chart } from 'chart.js';

When to Report Issues to Chart.js Maintainers

If you’ve tried all the solutions above and still encounter the MwoWUuIu.js 404 error, you should consider reporting it to the Chart.js maintainers. This is particularly warranted if:

1. The issue occurs with the official production build
2. Multiple developers report the same problem
3. The issue breaks Chart.js functionality
4. You can reproduce it consistently across different environments

The Chart.js GitHub repository is the appropriate place to report such issues, as evidenced by the various GitHub issues found in the research.

Conclusion

The MwoWUuIu.js 404 error in Chart.js is typically a source map configuration issue rather than a critical problem with the library itself. By following the solutions outlined above:

1. Use production builds instead of development versions in production
2. Configure proper imports for your specific framework
3. Avoid version conflicts by using consistent library versions
4. Consider local installation if CDN issues persist

Most developers can resolve this issue quickly by switching to the minified production version of Chart.js. Remember that while source map errors can be annoying in the console, they don’t typically affect the actual functionality of Chart.js - they’re primarily a debugging aid that can be safely disabled if needed.

For ongoing maintenance, always monitor the Chart.js releases page for updates and fixes related to these kinds of issues.

Sources

1. Salesforce StackExchange - 404 not found when loading chartjs library in lightning web components
2. Stack Overflow - 404 Not Found Error when trying to display a chart with Chart.js
3. Stack Overflow - DevTools failed to load source map, chart.js behaving abnormally
4. Chart.js GitHub Discussion - Understanding Devtools source map in Chart.js
5. Chart.js Documentation - Integration
6. 12 Days of Web - JS Import Maps
7. Microsoft Learn - Source Maps
8. Stack Overflow - Getting a 404 error when trying to use ng2-charts