Introduction

Query is a library built specifically for web components to make it easy to interact with a page’s DOM and shadow DOM in a chainable way.

Query includes many of the helpers which make it easy to interact with web components, emit and consume events, traverse the DOM tree, retreive common values and much more.

API Reference — For a more thorough explanation of functionality visit the API reference guide.

Why Create a Library

Web components are built around encapsulating portions of the DOM in the Shadow DOM, which prevent easy access or reference from other scopes.

Many common usage patterns for developers require traversing the DOM, but with native APIs these will stop at shadow DOM root or slotted content boundaries. Doing this deeply or recursively is also basically impossible without writing your own helpers.

Query helps give you all the utilities like closest, find, siblings but while giving you options for traversing these boundaries.

import { $$ } from '@semantic-ui/query'

// this will not return content in shadow dom
let el1 = document.querySelector('my-button .button');

// this will return content in shadow dom
const el2 = $$('my-button .button');

import { $$ } from '@semantic-ui/query'

// from inside a web component

// this will not return content in slot
let el1 = this.shadowRoot.querySelector('slot .content');

// this will return content in slot
const el2 = $$('slot .content', { root: this.shadowRoot });

Accessing DOM

Query provides two exports $ and $$.

$ is used for querying the normal browser DOM and $$ is for querying the shadow DOM (the DOM present in web components).

$ - Standard DOM

$ is designed to allow for extremely performant chaining for normal DOM nodes.

$ Performance - Query uses native querySelector and modern DOM APIs which means the performance implications are low when using $.

import { $ } from '@semantic-ui/query';

const $div = $('div');

$$ - Shadow DOM

$$ allows for accessing DOM nodes regardless of where they are in the page.

Web components have portions of their DOM encapsulated in what is known as the Shadow DOM which can only be accessed with el.shadowRoot.querySelector, and portions of shadow DOM have content slots which can only access content via el.slottedNodes.

The $$ helps traverse these boundaries to access children or parent nodes in a way similar to $.

$$ Performance - $$ must pierce shadow DOM boundaries recursively which can reduce perfomance over $. For most use-cases this difference is negligible (less than 1ms), but for complex DOM trees the cost can be more significant. For this reason it is recommended to use $$ only when necessary to avoid performance roadblocks in your app.

DOM Example

The following example shows the difference in selectors between $ and $$ from inside a web component.

Chaining

Query is built on the concept of chaining, which was originally pioneered by jQuery, where method can be called in a pipeline processing the results of previous method calls.

import { $ } from '@semantic-ui/query';

const pText = $('div').find('p').text();

To see more examples of chaining browse the Query API docs.

Additional Options

You can specify additional options when initializing the Query class.

Root

In some advanced cases you might want to limit Query to a particular root element.

// special $ scoped to my-root for some custom app
const $ = function (selector) {
  const myRoot = $('my-component').el().shadowRoot;
  return new Query(selector, { root: myRoot });
};

Pierce Shadow

$$ is the same as passing pierceShadow: true as an option to $ but is provided for convenience as a separate export.

import { $, $$ } from '@semantic-ui/query';

// these are equivalent
const $div = $$('my-component div');
const $div = $('my-component div', { pierceShadow: true});

Usage

Browser

In a browser environment you can use exportGlobals to export $ and $$ for use in your page. For more fine grained control see the browser helpers section below

import { exportGlobals } from '@semantic-ui/query';

// make $ and $$ available globally
exportGlobals();

Components

$ and $$ are integrated into all lifecycle callbacks and events in Semantic UI components.

const createComponent = ({$, $$}) => ({
  getDiv() {
    return $('div').get(0);
  }
});

const onCreated = ({$, $$}) => {
  const $div = $('div');
};

const events =  {
  'click div'({$ , $$}) {
    const $div = $('div').trigger('click');
  }
};

Browser Helpers

A few additional helpers are provided specifically for using Query in browser environments.

For more information see the API reference.

Restoring Globals

If you need to restore the previous values before calling export globals.

import { exportGlobals, restoreGlobals } from '@semantic-ui/query';

// $ and $$ are defined
exportGlobals();

// $ and $$ are now their original values
restoreGlobals();

Custom Aliases

You can also choose to use Query as a custom alias

import { useAlias } from '@semantic-ui/query';

const myQuery = useAlias();
const $div = myQuery('div');