Elastic Tabs

1"use client"
2 
3import * as React from "react"
4 
5import { cn } from "@/lib/utils"
6 
7export interface ElasticTabsItem {
8  value: string
9  label: React.ReactNode
10}
11 
12export interface ElasticTabsProps extends Omit<
13  React.ComponentProps<"div">,
14  "onChange"
15> {
16  /** The tabs, in order. */
17  items: ElasticTabsItem[]
18  /** Selected tab. Leave it out to let the group own the selection. */
19  value?: string
20  /** Starting tab when the group owns the selection. */
21  defaultValue?: string
22  /** Called with the value of the tab moved to. */
23  onValueChange?: (value: string) => void
24  /** Length of the whole travel, in milliseconds. */
25  duration?: number
26}
27 
28const EMPTY = { left: 0, width: 0 }
29 
30export function ElasticTabs({
31  items,
32  value,
33  defaultValue,
34  onValueChange,
35  duration = 280,
36  className,
37  ...props
38}: ElasticTabsProps) {
39  const [own, setOwn] = React.useState(defaultValue ?? items[0]?.value)
40  const isControlled = value !== undefined
41  const active = isControlled ? value : own
42  const index = Math.max(
43    items.findIndex((item) => item.value === active),
44    0
45  )
46 
47  const listRef = React.useRef<HTMLDivElement>(null)
48  const tabsRef = React.useRef<(HTMLButtonElement | null)[]>([])
49  const [pill, setPill] = React.useState(EMPTY)
50  // The first placement is a measurement, not a move, so it must not travel.
51  const [settled, setSettled] = React.useState(false)
52 
53  const measure = React.useCallback((position: number) => {
54    const tab = tabsRef.current[position]
55    return tab ? { left: tab.offsetLeft, width: tab.offsetWidth } : EMPTY
56  }, [])
57 
58  const indexRef = React.useRef(index)
59  indexRef.current = index
60  const pillRef = React.useRef(EMPTY)
61  React.useEffect(() => {
62    pillRef.current = pill
63  }, [pill])
64 
65  // Placement. Runs once on mount and again whenever the row is resized, so a
66  // wrapped or re-laid-out group never leaves the pill behind.
67  React.useEffect(() => {
68    const list = listRef.current
69    if (!list) {
70      return
71    }
72 
73    const observer = new ResizeObserver(() =>
74      setPill(measure(indexRef.current))
75    )
76    observer.observe(list)
77 
78    const timer = window.setTimeout(() => setSettled(true), 0)
79    return () => {
80      observer.disconnect()
81      window.clearTimeout(timer)
82    }
83  }, [measure])
84 
85  // Travel. The pill first stretches to cover both tabs, then contracts onto
86  // the new one. Moving `left` and `width` straight to the target slides a
87  // fixed shape across. Spanning first is what makes it read as elastic.
88// … truncated