Async Script Loader

Allows asynchronous loading of scripts and styles in a Single Page Application (or anything else, in fact):

• Using a test to ensure that the code is only loaded once
• Running a callback once the script is loaded
• Running a callback if the script is already loaded
• Not blocking the main thread

Reasoning

Having integrated a multitude of third-party SDKs from large, well known providers, I've come to the conclusion that not having a standard interface turns the whole thing into a minefield of callbacks, timers, random library-specific loader modules, and global objects on the window, resulting in XSS risks and all sort of other undesirable behaviour. This module aims to provide a standard way of loading third-party dependencies.

Usage

You pass a list of urls to the loader, along with a method for checking that your page is ready, and a callback to call when it is.

Urls can be scripts or stylesheets.

Script Tags

You can use the module like so, for a library loaded from example.com, which, when loaded, adds an attribute called PROVIDER to the global window object.

<script>
  import loader from '@beyonk/async-script-loader'

  const url = '//example.com/sdk/1.0.0/lib.js'

  function test () {
    return !!window.PROVIDER
  }

  function callback () {
    window.PROVIDER.someFunction()
  }

  loader([
    { type: 'script', url }
  ], test, callback)
</script>

You can pass options for script tags.

<script>
  loader([
    { type: 'script', url, options: { async: true, defer: true } } // these are the default options
  ], test, callback)
</script>

Style Tags

You can include any number of tags, including style tags.

When the last one has loaded, the callback will be called.

<script>
  import loader from '@beyonk/async-script-loader'

  loader([
    { type: 'script', url: '//example.com/sdk/1.0.0/lib.js' },
    { type: 'script', url: '//example.com/sdk/1.0.0/lib2.js' },
    { type: 'style', url: '//example.com/sdk/1.0.0/style.css' }
  ], () => {
    return !!window.PROVIDER
  }, () => {
    window.PROVIDER.someFunction()
  })
</script>

No more tears!

Inline scripts / Inline css

You can use inline content for either type of tag by passing the configuration attribute content instead of url. This will write the content passed into the tag's body rather than setting it as an href or src attribute url will always take prescidence, so leave it out for content to work.

<script>
  import loader from '@beyonk/async-script-loader'

  loader([
    { type: 'script', content: 'console.log("foo");' },
    { type: 'style', content: '* { color: red; }' }
  ],
  () => false, // always load
  () => () // no-op
)
</script>