The :defined
CSS pseudo-class represents any element that has been defined. This includes any standard element built in to the browser, and custom elements that have been successfully defined (i.e. with the CustomElementRegistry.define()
method).
/* Selects any defined element */ :defined { font-style: italic; } /* Selects any instance of a specific custom element */ simple-custom:defined { display: block; }
Syntax
:defined
Examples
This example first includes a script defining a <simple-custom>
custom element:
customElements.define('simple-custom', class extends HTMLElement { constructor() { super(); let divElem = document.createElement('div'); divElem.textContent = this.getAttribute('text'); let shadowRoot = this.attachShadow({mode: 'open'}) .appendChild(divElem); } })
Next, we have some HTML with an instance of the <simple-custom>
element, and a standard <p>
element:
<simple-custom text="Custom element example text"></simple-custom> <p>Standard paragraph example text</p>
Now for some CSS. Here we define background colors based on element types, change the opacity of the custom element based on whether or not it is defined, and use the :defined
selector to make all defined element text appear in italic.
/* Give the two elements distinctive backgrounds */ p { background: yellow; } simple-custom { display: block; background: cyan; } /* Both the custom and the built-in element are given italic text */ :defined { font-style: italic; }
Finally, we provide the following two rules to hide any instances of our custom element that are not defined, and display instances that are defined as block level elements:
simple-custom:not(:defined) { opacity: 0; } simple-custom:defined { opacity: 0.75; text-decoration: underline; }
This is useful if you have a complex custom element that takes a while to load into the page — you might want to hide instances of the element until definition is complete, so that you don't end up with flashes of ugly unstyled elements on the page.
Result
Here is the result of running the code above:
Specifications
Specification | Status | Comment |
---|---|---|
HTML Living Standard The definition of ':defined' in that specification. |
Living Standard |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
:defined | Chrome Full support 54 | Edge No support No | Firefox Full support 63 | IE No support No | Opera Full support 41 | Safari Full support 10 | WebView Android Full support 54 | Chrome Android Full support 54 | Firefox Android Full support 63 | Opera Android Full support 41 | Safari iOS Full support 10 | Samsung Internet Android Full support 6.0 |
Legend
- Full support
- Full support
- No support
- No support