Frontend & browser·Storage and platform APIs
you defined a tag with a dash in it and used it in HTML like any built-in element.
Custom element
Also calledweb component, customElements.define
A user-defined HTML element with its own lifecycle callbacks, registered under a hyphenated name. It is framework-independent and long-lived, which makes it the right vehicle for a design system shared across applications with different stacks. The rough edges are real: attributes are strings, passing rich data and events across the boundary is awkward, and server rendering one is still not straightforward.