jQuery Plugins and Legacy Applications

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Inside Webpack, when you require a module, it does not (usually) set a global variable. Instead, it just returns a value:

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        // this loads jquery, but does *not* set a global $ or jQuery variable
const $ = require('jquery');
    

In practice, this will cause problems with some outside libraries that rely on jQuery to be global or if your JavaScript isn't being processed through Webpack (e.g. you have some JavaScript in your templates) and you need jQuery. Both will cause similar errors:

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        Uncaught ReferenceError: $ is not defined at [...]
Uncaught ReferenceError: jQuery is not defined at [...]
    

The fix depends on what code is causing the problem.

Fixing jQuery Plugins that Expect jQuery to be Global

jQuery plugins often expect that jQuery is already available via the $ or jQuery global variables. To fix this, call autoProvidejQuery() from your webpack.config.js file:

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        Encore
    // ...
+     .autoProvidejQuery()
;
    

After restarting Encore, Webpack will look for all uninitialized $ and jQuery variables and automatically require jquery and set those variables for you. It "rewrites" the "bad" code to be correct.

Internally, this autoProvidejQuery() method calls the autoProvideVariables() method from Encore. In practice, it's equivalent to doing:

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        Encore
    // you can use this method to provide other common global variables,
    // such as '_' for the 'underscore' library
    .autoProvideVariables({
        $: 'jquery',
        jQuery: 'jquery',
        'window.jQuery': 'jquery',
    })
    // ...
;
    

Accessing jQuery from outside of Webpack JavaScript Files

If your code needs access to $ or jQuery and you are inside of a file that's processed by Webpack/Encore, you should remove any "$ is not defined" errors by requiring jQuery: var $ = require('jquery').

But if you also need to provide access to $ and jQuery variables outside of JavaScript files processed by Webpack (e.g. JavaScript that still lives in your templates), you need to manually set these as global variables in some JavaScript file that is loaded before your legacy code.

For example, in your app.js file that's processed by Webpack and loaded on every page, add:

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        // require jQuery normally
const $ = require('jquery');

+ // create global $ and jQuery variables
+ global.$ = global.jQuery = $;
    

The global variable is a special way of setting things in the window variable. In a web context, using global and window are equivalent, except that window.jQuery won't work when using autoProvidejQuery(). In other words, use global.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.

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