jQuery and Legacy Applications

jQuery and Legacy Applications

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. It will be a problem if some of your JavaScript isn't being processed through Webpack (e.g. you have some JavaScript in your templates).

Using Libraries that Expect jQuery to be Global

Some legacy JavaScript applications use programming practices that don't play well with the new practices promoted by Webpack. The most common of these problems is using code (e.g. jQuery plugins) that assume that jQuery is already available via the the $ or jQuery global variables. If those variables are not defined, you'll get these errors:

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

Instead of rewriting everything, Encore allows for a different solution. Thanks to the autoProvidejQuery() method, whenever a JavaScript file uses the $ or jQuery variables, Webpack automatically requires jquery and creates those variables for you.

So, when working with legacy applications, you may need to add the following to webpack.config.js:

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

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 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, you could define a common.js file that's processed by Webpack and loaded on every page with the following content:

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

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

Tip

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.