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Webpack ProvidePlugin vs externals?

I'm exploring the idea of using Webpack with Backbone.js.

I've followed the quick start guide and has a general idea of how Webpack works, but I'm unclear on how to load dependency library like jquery / backbone / underscore.

Should they be loaded externally with <script> or is this something Webpack can handle like RequireJS's shim?

According to the webpack doc: shimming modules, ProvidePlugin and externals seem to be related to this (so is bundle! loader somewhere) but I cannot figure out when to use which.

Thanks

Solution

  • It's both possible: You can include libraries with a <script> (i. e. to use a library from a CDN) or include them into the generated bundle.

    If you load it via <script> tag, you can use the externals option to allow to write require(...) in your modules.

    Example with library from CDN:

    <script src="https://code.jquery.com/jquery-git2.min.js"></script>

// the artifial module "jquery" exports the global var "jQuery"
externals: { jquery: "jQuery" }

// inside any module
var $ = require("jquery");

    Example with library included in bundle:

    copy `jquery-git2.min.js` to your local filesystem

// make "jquery" resolve to your local copy of the library
// i. e. through the resolve.alias option
resolve: { alias: { jquery: "/path/to/jquery-git2.min.js" } }

// inside any module
var $ = require("jquery");

    The ProvidePlugin can map modules to (free) variables. So you could define: "Every time I use the (free) variable xyz inside a module you (webpack) should set xyz to require("abc")."

    Example without ProvidePlugin:

    // You need to require underscore before you can use it
var _ = require("underscore");
_.size(...);

    Example with ProvidePlugin:

    plugins: [
  new webpack.ProvidePlugin({
    "_": "underscore"
  }) 
]

// If you use "_", underscore is automatically required
_.size(...)

    Summary:

    • Library from CDN: Use <script> tag and externals option
    • Library from filesystem: Include the library in the bundle. (Maybe modify resolve options to find the library)
    • externals: Make global vars available as module
    • ProvidePlugin: Make modules available as free variables inside modules