Uncaught SyntaxError: Unexpected end of input in Django Template (inline JS)

I'm developing a Django web application to visualize data from uploaded XML files. I'm encountering a persistent Uncaught SyntaxError: Unexpected end of input in the browser console when loading the data visualization page. This error prevents the JavaScript from running and the chart (using Chart.js) from displaying.

Problem:

When I navigate to the /visualizer/data-visualizer/ page, the browser console shows Uncaught SyntaxError: Unexpected end of input, pointing to a line number within the main HTML response (e.g., data-visualizer/:3149:80). The chart area on the page remains blank.

Context:

  • Django Version: 5.2
  • Python Version: [Your Python version, e.g., 3.9, 3.10]
  • Operating System: Windows
  • Web Server: Django Development Server (manage.py runserver)
  • The application workflow is: Upload XML file -> Select data fields -> View visualization page (/visualizer/data-visualizer/).
  • The visualization page is rendered by the VisualizerInterfaceView using the visualizer_interface.html template.
  • The template includes Chart.js via a CDN and has an inline <script> block containing custom JavaScript logic to retrieve data from JSON embedded in the template and render the chart.

Observed Behavior and Debugging Steps Taken:

  1. The Uncaught SyntaxError: Unexpected end of input error appears consistently in the browser console (tested in Chrome and Edge).
  2. Looking at the browser's "View Page Source" for the /visualizer/data-visualizer/ page reveals that the inline JavaScript code within the <script> block is being cut off/truncated at the very end. This missing code includes closing curly braces, parentheses, the }); for the DOMContentLoaded listener, and the closing </script> tag.
  3. I have visually confirmed multiple times that the visualizer_interface.html file on my local disk contains the complete and correct JavaScript code, including all the necessary closing elements. I have opened the file in a separate editor instance to verify its content on disk.
  4. Restarting the Django development server does not resolve the issue.
  5. Performing aggressive browser cache clearing and hard refreshes does not resolve the issue.
  6. Trying a different browser (Edge) also shows the exact same SyntaxError and truncation.
  7. The Django development server terminal output shows a GET /visualizer/data-visualizer/ HTTP/1.1" 200 ... response, indicating the page is being served without explicit server-side errors at that stage.
  8. A separate issue related to saving uploaded files to the media/datasets directory was debugged and resolved, confirming that basic file saving/writing works in the project now.

Relevant Code:

(Please include the full, correct code for your visualizer_interface.html here. This is the code you confirmed is complete on your disk.)

{% extends 'base.html' %}
{% comment %} visualizer_interface.html {% endcomment %}
{% load custom_filters %} {# Make sure you have custom_filters.py with the get_item filter and load it here #}
{% load static %}

{% block title %}Data Visualizer{% endblock %}

{# Page-specific CSS, including basic table and chart container styles #}
{% block extra_css %}
    {# You can uncomment the link below if you have a static css/visualizer_interface.css file #}
    {# <link rel="stylesheet" href="{% static 'css/visualizer_interface.css' %}"> #}
    <style>
        /* Basic styling for the table */
        table {
            border-collapse: collapse;
            width: 100%;
            margin-top: 20px;
        }
        th, td {
            border: 1px solid #ddd;
            padding: 8px;
            text-align: left;
        }
        th {
            background-color: #f2f2f2;
        }
        /* Style for the chart container */
        .chart-container {
            position: relative; /* Needed for Chart.js responsiveness */
            width: 80%; /* Adjust as needed */
            margin: 20px auto; /* Center the chart */
            height: 400px; /* Give the container a height */
        }
         /* Optional: Style for messages */
        .messages {
            list-style: none;
            padding: 0;
            margin: 10px 0;
        }
        .messages li {
            padding: 10px;
            margin-bottom: 5px;
            border-radius: 4px;
        }
        .messages .success {
            background-color: #d4edda;
            color: #155724;
            border: 1px solid #c3e6cb;
        }
        .messages .error {
            background-color: #f8d7da;
            color: #721c24;
            border: 1px solid #f5c6cb;
        }
         .messages .info {
            background-color: #d1ecf1;
            color: #0c5460;
            border: 1px solid #bee5eb;
        }
    </style>
{% endblock %}


{% block content %}
<div class="container mt-4">
    <h2>Data Visualizer</h2>

    {# Display messages #}
    {% if messages %}
        <ul class="messages">
            {% for message in messages %}
                <li{% if message.tags %} class="{{ message.tags }}"{% endif %}>{{ message }}</li>
            {% endfor %}
        </ul>
    {% endif %}


    {# Section to display extracted data in a table #}
    <h3>Extracted Data Preview:</h3>
    {% if extracted_data %}
        <table class="table table-bordered table-striped">
            <thead>
                <tr>
                    {# Display the extracted data field names as headers #}
                    {% for field in chart_data_fields %}
                        <th>{{ field }}</th>
                    {% endfor %}
                </tr>
            </thead>
            <tbody>
                {# Iterate through the extracted data entries (rows) #}
                {% for row in extracted_data %}
                    <tr>
                        {# Iterate through the fields for each row #}
                        {% for field in chart_data_fields %}
                            {# Access data using the field name as the key #}
                            {# Use the get_item filter defined in custom_filters.py #}
                            <td>{{ row|get_item:field }}</td>
                        {% endfor %}
                    </tr>
                {% endfor %}
            </tbody>
        </table>
    {% else %}
        <p>No data has been extracted yet. Please upload an XML file and select data fields.</p>
         <p><a href="{% url 'visualizer:upload_dataset' %}">Upload New File</a></p>
    {% endif %}

    {# Charting Section #}
    {% if extracted_data %} {# Only show chart section if data is available #}
        <hr> {# Horizontal rule for separation #}
        <h3>Chart Options:</h3>
        <div class="mb-3"> {# Margin bottom #}
            <label for="chartType" class="form-label">Chart Type:</label>
            <select id="chartType" class="form-select d-inline-block w-auto"> {# w-auto for bootstrap #}
                <option value="bar">Bar Chart (Amount by Type)</option>
                <option value="line">Line Chart (Amount over Time - Requires Date Handling)</option>
                <option value="pie">Pie Chart (Total Amount by Type)</option>
                <option value="doughnut">Doughnut Chart (Total Amount by Type)</option>
                {# Add other relevant chart types if needed #}
            </select>

            <label for="chartColor" class="form-label ms-3">Chart Color:</label> {# margin start #}
            <input type="color" id="chartColorInput" value="#007bff" class="form-control-color d-inline-block"> {# Default blue color, form-control-color for bootstrap #}
        </div>

        <h3>Data Chart:</h3>
        <div class="chart-container">
            {# Canvas element where the chart will be rendered #}
            <canvas id="myChart"></canvas>
        </div>
    {% endif %}


</div> {# closes <div class="container mt-4"> #}

{# Safely embed JSON data for JavaScript - Place these lines HERE within block content, outside the container div #}
{{ extracted_data|json_script:"extractedDataJson" }}
{{ chart_data_fields|json_script:"chartDataFieldsJson" }}

{% endblock %} {# End of block content #}




  [1]: https://i.sstatic.net/fzzjiBp6.png
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