เจเนอริกของคอมโพเนนต์ — เบื้องต้น

บทนำ

รายการทั่วไป<T>

import React from "react"

type ListProps<T> = { items: T[]; render: (item: T, index: number) => React.ReactNode }

export function List<T>({ items, render }: ListProps<T>) {
  return <div style={{ display: "grid", gap: 6 }}>{items.map(render)}</div>
}

export default function App() {
  return (
    <div style={{ display: "grid", gap: 12 }}>
      <List<number> items={[1,2,3]} render={(n) => <span>#{n}</span>} />
      <List<{ id: string; name: string }>
        items={[{ id: "u1", name: "Ada" }, { id: "u2", name: "Lin" }]}
        render={(u) => <strong>{u.name}</strong>}
      />
    </div>
  )
}

ข้อจำกัดด้วย extends

import React from "react"

type Keyed = { id: string }

type KeyListProps<T extends Keyed> = { items: T[]; render: (item: T) => React.ReactNode }

export function KeyList<T extends Keyed>({ items, render }: KeyListProps<T>) {
  return (
    <ul>
      {items.map((x) => (
        <li key={x.id}>{render(x)}</li>
      ))}
    </ul>
  )
}

export default function App() {
  const users = [{ id: "u1", name: "Ada" }, { id: "u2", name: "Lin" }]
  return <KeyList items={users} render={(u) => <span>{u.name}</span>} />
}

การอนุมาน T

import React from "react"

type GridProps<T> = { items: T[]; columns?: number; render: (item: T) => React.ReactNode }

export function Grid<T>({ items, columns = 2, render }: GridProps<T>) {
  const css = { display: "grid", gridTemplateColumns: `repeat(${columns}, 1fr)`, gap: 8 }
  return <div style={css as React.CSSProperties}>{items.map(render)}</div>
}

export default function App() {
  const products = [
    { sku: "p1", title: "Mouse", price: 25 },
    { sku: "p2", title: "Keyboard", price: 80 }
  ]
  // T is inferred from products; no need to annotate
  return <Grid items={products} render={(p) => <span>{p.title} — ${p.price}</span>} />
}

ตัวช่วยการเรนเดอร์

import React from "react"

type Render<T> = (item: T) => React.ReactNode

type TableProps<T extends { id: string }> = { items: T[]; renderRow: Render<T> }

export function Table<T extends { id: string }>({ items, renderRow }: TableProps<T>) {
  return (
    <table>
      <tbody>
        {items.map((x) => (
          <tr key={x.id}><td>{renderRow(x)}</td></tr>
        ))}
      </tbody>
    </table>
  )
}

export default function App() {
  const rows = [ { id: "1", label: "One" }, { id: "2", label: "Two" } ]
  return <Table items={rows} renderRow={(r) => <span>{r.label}</span>} />
}

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