UglifyJS Options Not Being Set in Flask App Using Flask-Assets: A Solution

When using Flask-Assets to manage static assets in a Flask application, setting UglifyJS options can be a bit tricky. In this article, we’ll explore the common issue of UglifyJS options not being set and provide a solution to overcome this problem.

The Problem

When trying to set UglifyJS options in a Flask app using Flask-Assets, you might encounter an issue where the options are not being applied. This can be frustrating, especially when you need to optimize your JavaScript code for production.

Example Code

Here’s an example of how you might try to set UglifyJS options in your Flask app:

from flask_assets import Bundle, Environment

bundles = {
    'js': Bundle(
        'js/app.js',
        filters='uglifyjs',
        output='gen/app.js'
    )
}

assets = Environment(app)
assets.register(bundles)

However, even with this setup, you might find that the UglifyJS options are not being applied to your JavaScript code.

The Solution

The solution lies in how you configure the UglifyJS filter in Flask-Assets. To set UglifyJS options, you need to pass a dictionary of options to the `uglifyjs` filter.

Corrected Code

Here’s the corrected code that sets UglifyJS options:

from flask_assets import Bundle, Environment

bundles = {
    'js': Bundle(
        'js/app.js',
        filters='uglifyjs',
        output='gen/app.js',
        uglifyjs_opts={
            'ecma': 6,
            ' warnings': True,
            'mangle': True,
            'safari10': True
        }
    )
}

assets = Environment(app)
assets.register(bundles)

In this example, we’ve added an `uglifyjs_opts` dictionary that contains the desired UglifyJS options. These options will now be applied to your JavaScript code when it’s processed by UglifyJS.

Conclusion

By following this solution, you should now be able to set UglifyJS options in your Flask app using Flask-Assets. Remember to pass a dictionary of options to the `uglifyjs` filter, and you’ll be able to optimize your JavaScript code for production.

I hope this helps! If you have any further questions, feel free to ask in the comments.

Frequently Asked Question

Got stuck with UglifyJS options not being set in your Flask app using Flask-Assets? Don’t worry, we’ve got you covered! Here are some frequently asked questions and answers to help you troubleshoot the issue.