ES6 makes it easy to declare external dependencies with import, but in order to avoid blocking rendering, HTML needs a way to import modules only in the context of asynchronously loaded code.

The module tag not only makes it convenient to import modules asynchronously, it improves the overall web programming model by moving all JS development into modules. The slogan to live by is:

<module> is a better <script>

In other words, all code -- even top level or bootstrapping code -- should live within modules. For convenience, top-level modules that are only executed to kick off an application don't need to be given names. But they still have the benefits of modules:

• they can declaratively import from other modules
• they're defined in a nested scope, making top-level IIFE boilerplate a thing of the past
• they're implicitly strict, eliminating some of the most egregious misfeatures (e.g., with) and interoperability hazards (e.g., block-local function declarations) of legacy JS

To understand the design and how you might build apps with the module tag, see the explainer document.