TOPICS

Introduction
Scenario
Use Generics: <T>
Final Source Code
Code Playground

Introduction

Often we need to create generic components in React / TypeScript that need to accept any kind of type.

Since we want to create reusable components and, at the same time, they should be type-safed too, we cannot define its own props as any type, and unknown is not often a valid solution.

Interacive Demo

WebSite

Youtube

Twitch

Visit WebSite

Scenario

Now let's imagine if we have to create a TabBar component in React/TypeScript that accepts an items property of any type of array(string[], User[], Whatever[]):

<TabBar
  items={anyTypeOfArray}
  onTabClick={selectHandler}
/>

The output:

Demo

If the TabBar items property should accept any kind of type we may think to use any[]. Right? Ehm... no 😅 We completely lose type checking!

interface TabBarProps<T> {
  items: any[];
  selectedItem: any;
  onTabClick: (item: any, selectedIndex: number) => void
}

In fact, by using any, the TypeScript compiler and your IDE/editor are not able to know which type of parameters your onTabClick will come back or what type of data selectedItem should accepts:

Ide problem

Use Generics: `<T>`

Instead of using any we can pass a generic type to our component:

First, we create a custom type (in this example MySocial but it could be anything):

interface MySocial {
  id: number;
  name: string;
  link: string;
}

const socials: MySocial[] = [
  { id: 11, name: 'WebSite', link: 'https://www.fabiobiondi.dev'},
  { id: 12, name: 'Youtube', link: 'https://www.youtube.com/c/FabioBiondi'},
  { id: 13, name: 'Twitch', link: 'https://www.twitch.tv/fabio_biondi'},
]

We can pass this type to the component as generic:

<TabBar<MySocial>
  selectedItem={selectedSocial}
  items={socials}
  onTabClick={selectHandler}
/>

Our TabBar component should now use generics instead of any. We can also decide this type must includes id and name in its definition:

interface TabBarProps<T> {
  items: T[];
  selectedItem: T;
  onTabClick: (item: T, selectedIndex: number) => void
}

export function TabBar<T extends { id: number, name: string}>(props: TabBarProps<T>) {
  
  /* ... your component code here ... */

}

Final Source Code

Here the complete source code of TabBar (it uses Tailwind for CSS but it doesn't matter) :

TabBar.tsx

interface TabBarProps<T> {
  items: T[];
  selectedItem: T;
  onTabClick: (item: T, selectedIndex: number) => void
}

export function TabBar<T extends { id: number, name: string}>(props: TabBarProps<T>) {
  const { items, selectedItem, onTabClick} = props;
  return (
    <>
      <div className="flex gap-x-3">
        {
          items.map((item, index) => {
            const activeCls = item.id === selectedItem.id ? 'bg-slate-500 text-white' : ' bg-slate-200';
            return <div
                key={item.id}
                className={'py-2 px-4 rounded ' + activeCls}
                onClick={() => onTabClick(item, index)}
              >
                {item.name}
              </div>
            }
          )
        }
      </div>
    </>
  )
}

Usage

Following an example of usage:

App.tsx

import { useState } from 'react';
import { TabBar } from '../../../shared/components/TabBar';

interface MySocial {
  id: number;
  name: string;
  link: string;
}

const socials: MySocial[] = [
  { id: 11, name: 'WebSite', link: 'fabiobiondi.dev'},
  { id: 12, name: 'Youtube', link: 'YT'},
  { id: 13, name: 'Twitch', link: 'twitch'},
]

export const App = () => {
  const [selectedSocial, setSelectedSocial] = useState<MySocial>(socials[0])

  function selectHandler(item: MySocial, selectedIndex: number) {
    setSelectedSocial(item)
  }

  return (
    <div>
      <h1>Tabbar Demo</h1>
        <TabBar<MySocial>
          selectedItem={selectedSocial}
          items={socials}
          onTabClick={selectHandler}
        />

      <div className="border border-slate-200 border-solid rounded my-3 p-5">
        <a href={selectedSocial.link}>Visit {selectedSocial.name}</a>
      </div>
    </div>
  )
};