Customized built-in elementsLimited availability
Customized built-in elements are HTML elements that extend built-in elements using the is attribute, to add new behaviors that you define.
Not yet supported in all major browsers — check the table and provide a fallback.
Browser support
DesktopChrome
1–66Not supported
67+Supportedsince May 29, 2018
Current: 155Edge
12–18Not supported
79+Supportedsince Jan 15, 2020
Current: 154Firefox
1–62Not supported
63+Supportedsince Oct 23, 2018
Current: 157Safari
✕Not supportedup to 27
Current: 27MobileChrome Android
18–66Not supported
67+Supportedsince May 31, 2018
Current: 155Firefox Android
4–62Not supported
63+Supportedsince Oct 23, 2018
Current: 157Safari iOS
✕Not supportedup to 27
Current: 27How to use
Not supported in Safari, Safari iOS. Use feature detection below and provide a fallback (or a polyfill) for those browsers.
Example
Full syntax and examples are on MDN: define#defining a customized built-in element.
Feature detection
JS · check before using
if ("CustomElementRegistry" in globalThis && "builtin_element_support" in CustomElementRegistry.prototype) {
// CustomElementRegistry.builtin_element_support is available
}Documentation (MDN)
Specification
Sub-features
Support for each part of the feature (2). The overall table above shows when the whole feature works.
| Sub-feature | Chrome | Edge | Firefox | Safari | Chrome Android | Firefox Android | Safari iOS |
|---|---|---|---|---|---|---|---|
| CustomElementRegistry.builtin_element_support | 67 | 79 | 63 | ✕ | 67 | 63 | ✕ |
| is | 67 | 79 | 63 | ✕ | 67 | 63 | ✕ |