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import { customElement, property, query, state } from "lit/decorators.js"
import { repeat } from "lit/directives/repeat.js"
import { classMap } from "lit/directives/class-map.js"
import style from "./style.scss?inline"
/**
* Option definition consumed by {@link VgDropdown}.
*/
export interface DropdownOption {
/**
* Display label shown to the user.
*/
label: string
/**
* Value returned when the option is selected.
*/
value: string
/**
* Optional helper text displayed beneath the option label.
*/
description?: string
/**
* Marks the option as disabled within the dropdown list.
*/
disabled?: boolean
}
/**
* Detail payload for the {@link VgDropdown} change event.
*/
export interface DropdownChangeDetail {
/**
* Selected option value.
*/
readonly value: string
/**
* Full option object corresponding to the selected value, when available.
*/
readonly option?: DropdownOption
/**
* Original change event from the native `<select>` element.
*/
readonly originalEvent: Event
}
let dropdownId = 0
const nextDropdownId = () => `vg-dropdown-${++dropdownId}`
/**
* Theme-aware dropdown select element supporting helper text, errors, and descriptions per option.
*
* @tag vg-dropdown
* @tagname vg-dropdown
* @summary The Dropdown component, used for selecting options from a list.
*
* @slot prefix - Optional slot rendered before the native select
* @slot suffix - Optional slot rendered after the native select (for badges, icons, etc.)
*
* @csspart select - Allows you to style the select element
* @csspart label - Allows you to style the label element
*
* @fires {DropdownChangeDetail} vg-change - Emitted when the selected option changes
*
*/
@customElement("vg-dropdown")
export class VgDropdown extends LitElement {
static styles = unsafeCSS(style)
/**
* Label displayed above the dropdown control.
*/
@property({ type: String })
public label: string | null = null
/**
* Optional text rendered below the control for guidance.
*/
@property({ type: String, attribute: "helper-text" })
public helperText: string | null = null
/**
* Error message displayed below the control; marks the dropdown as invalid.
*/
@property({ type: String })
public error: string | null = null
/**
* Placeholder rendered as the first option when no value is selected.
*/
@property({ type: String })
public placeholder: string | null = null
/**
* Currently selected value.
*/
@property({ type: String })
public value: string | null = null
/**
* Name attribute forwarded to the native select element.
*/
@property({ type: String })
public name: string | null = null
/**
* Disables the dropdown and prevents user interaction.
*/
@property({ type: Boolean, reflect: true })
public disabled = false
/**
* Marks the dropdown as required when used in forms.
*/
@property({ type: Boolean, reflect: true })
public required = false
/**
* Collection of options rendered by the dropdown.
*/
@property({ attribute: false })
public options: DropdownOption[] = []
@query("select")
private selectElement!: HTMLSelectElement
@state()
private hasPrefixContent = false
@state()
private hasSuffixContent = false
private readonly dropdownId = nextDropdownId()
protected firstUpdated() {
this.updateSlotState("prefix")
this.updateSlotState("suffix")
}
protected updated() {
if (this.selectElement) {
const desired = this.value ?? ""
Iif (this.selectElement.value !== desired) {
this.selectElement.value = desired
}
}
}
/**
* @inheritdoc
*/
protected render() {
const classes = {
control: true,
"has-prefix": this.hasPrefixContent,
"has-suffix": this.hasSuffixContent,
"has-error": !!this.error,
}
const describedBy = [
this.helperText ? `${this.dropdownId}-helper` : null,
this.error ? `${this.dropdownId}-error` : null,
].filter((value): value is string => value !== null)
return html`
<label class="field" for=${this.dropdownId}>
${this.label ? html`<span class="field__label">${this.label}</span>` : null}
<div class=${classMap(classes)}>
<slot name="prefix" @slotchange=${this.onSlotChange}></slot>
<select
id=${this.dropdownId}
name=${this.name ?? ""}
?disabled=${this.disabled}
?required=${this.required}
aria-invalid=${this.error ? "true" : "false"}
aria-describedby=${describedBy.join(" ")}
@change=${this.onChange}
>
${this.renderPlaceholder()}
${repeat(
this.options,
(option) => option.value,
(option) => html`
<option
value=${option.value}
?disabled=${option.disabled}
?selected=${option.value === this.value}
title=${option.description ?? ""}
>
${option.label}
</option>
`,
)}
</select>
<slot name="suffix" @slotchange=${this.onSlotChange}></slot>
</div>
${this.renderDescriptions()}
</label>
`
}
private renderPlaceholder() {
Iif (!this.placeholder) {
return null
}
const isSelected = !this.value
return html`<option value="" ?selected=${isSelected} disabled hidden>${this.placeholder}</option>`
}
private renderDescriptions() {
return html`
${this.helperText ? html`<p id=${`${this.dropdownId}-helper`} class="field__helper">${this.helperText}</p>` : null}
${this.error ? html`<p id=${`${this.dropdownId}-error`} class="field__error">${this.error}</p>` : null}
`
}
private onChange(event: Event) {
const target = event.target as HTMLSelectElement
this.value = target.value || null
const selected = this.options.find((option) => option.value === this.value)
this.dispatchEvent(new CustomEvent<DropdownChangeDetail>("vg-change", {
detail: {
value: this.value ?? "",
option: selected,
originalEvent: event,
},
// bubbles: true,
composed: true,
}))
}
private onSlotChange(event: Event) {
const slot = event.target as HTMLSlotElement
this.updateSlotState(slot.name as "prefix" | "suffix")
}
private updateSlotState(name: "prefix" | "suffix") {
const slot = this.shadowRoot?.querySelector(`slot[name="${name}"]`) as HTMLSlotElement | null
const hasContent = (slot?.assignedNodes({ flatten: true }).length ?? 0) > 0
if (name === "prefix" && this.hasPrefixContent !== hasContent) {
this.hasPrefixContent = hasContent
}
if (name === "suffix" && this.hasSuffixContent !== hasContent) {
this.hasSuffixContent = hasContent
}
}
}
declare global {
interface HTMLElementTagNameMap {
"vg-dropdown": VgDropdown
}
}
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