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Nairobi

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React devs KE 🇰🇪 Meetup February 2025 | Crafting Reusable Code with React & TypeScript: From Design to NPM

slides used in the presentation building the generic component In this example we'll use...

Date published

February 2, 2025

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© 2026 Dennis Waweru

Built from Nairobi with TypeScript

slides used in the presentation

Contents

01building the generic component
02publishing to npm
03The end

building the generic component

In this example we'll use a tale to demostrate how to build a generic component that adapts to any type of data

to go from a fully hardcoded componenst to a

more dynamic one

we first put the tables rows into an array and then pass that array to the component which we loop over to get the table rows

<video controls src="https://github.com/tigawanna/ReactDevsKe-Meetup-February-2025/raw/d45806eca0a9a6b67f047b439894905a0b712450/docs/rows-to-mapped-rows.mp4" title="rows-to-mapped-rows"></video>

And the same can also be done to the columns

<video controls src="https://github.com/tigawanna/ReactDevsKe-Meetup-February-2025/raw/d45806eca0a9a6b67f047b439894905a0b712450/docs/static-to-dynamic-coumns.mp4" title="static-to-dynamic-coumns"></video>

and now our table mponent can take in the data and the columns and then render the table rows and columns

tsx

1type Player = {
2  id: number;
3  name: string;
4  age: number;
5  rank: number;
6}
7
8type TableColumn = {
9  label: string;
10  accessor: keyof Player;
11};
12interface DynamicPlayerstableProps {
13  columns: Array<TableColumn>;
14  data: Array<Player>;
15}
16
17export function DynamicPlayerstable({data,columns}: DynamicPlayerstableProps) {
18    return ....
19}

Our players table component

is now decoupled from the data but we can take this further by decouping it from the shape of data. In it's current form it requires us to pass in data like this

tsx

1const columns: Array<TableColumn> = [
2  { label: "ID", accessor: "id" },
3  { accessor: "name", label: "Name" },
4  { accessor: "age", label: "Age" },
5  { accessor: "rank", label: "Rank" },
6];
7
8const data: Array<Player> = [
9  { id: 1, name: "Player1", age: 25, rank: "Silver" },
10  { id: 2, name: "Player2", age: 30, rank: "Gold" },
11  { id: 3, name: "Player3", age: 22, rank: "Bronze" },
12  { id: 4, name: "Player4", age: 28, rank: "Platinum" },
13  { id: 5, name: "Player5", age: 24, rank: "Diamond" },
14  { id: 6, name: "Player6", age: 27, rank: "Silver" },
15  { id: 7, name: "Player7", age: 29, rank: "Gold" },
16];
17return <DynamicPlayerstable columns={columns} data={data} />;

The table structure is dynamic enough to accomodate any array of objects we pass in with the only required field being od id because we use it as the key to every row

tsx

1<tbody>
2  {data.map((player) => (
3    <tr key={player.id}>
4      {columns.map((column) => (
5        <td key={column.accessor}>{player[column.accessor]}</td>
6      ))}
7    </tr>
8  ))}
9</tbody>

To accomplish this we'll need to use a generic type usuaally maerked as T which is a way to pass in variables to out types and interfaces

firdt we pass it into the component

tsx

1export function DynamicPlayerstable<T>({ data, columns }: DynamicPlayerstableProps);

then we pass it into our parameter interface

tsx

1interface DynamicPlayerstableProps<T> {
2  columns: Array<TableColumn>;
3  data: Array<Player>;
4}
5
6export function DynamicPlayerstable<T>({ data, columns }: DynamicPlayerstableProps<T>);

this type T should be the type of the object that we pass in to the array so we can now replace type Player with T

tsx

1interface DynamicPlayerstableProps<T> {
2  columns: Array<TableColumn>;
3  data: Array<T>;
4}

our TbaleColumn type was also relying on the type Player so the type is also going to change to TableColumn<T> so we can now replace type Player with T

<video controls src="https://github.com/tigawanna/ReactDevsKe-Meetup-February-2025/raw/d45806eca0a9a6b67f047b439894905a0b712450/docs/type-Player-to-T.mp4" title="type-Player-to-T"></video>

At this point typescipt will be able to give us auto complete for the coluns field based on what type T is based on the array we pass into the data field

with player rows array ![alt text](https://github.com/tigawanna/ReactDevsKe-Meetup-February-2025/raw/d45806eca0a9a6b67f047b439894905a0b712450/docs/player-autocomplete.png)

with teams row array ![alt text](https://github.com/tigawanna/ReactDevsKe-Meetup-February-2025/raw/d45806eca0a9a6b67f047b439894905a0b712450/docs/teams-autocomplete.png)

![alt text](https://github.com/tigawanna/ReactDevsKe-Meetup-February-2025/raw/d45806eca0a9a6b67f047b439894905a0b712450/docs/symbol-error.png) Out component is working fine from the outside but typescript is having a hader time understanding the types inside the component sine generice type T could be any type and it's keys could be numver|string|symbol , symbols aren't allowed as react keys so we can narrow that type by using an intersection & to inform typescrpt that the keys of T must be a string like we had in type Player

tsx

1type TableColumn<T> = {
2  label: string;
3  accessor: keyof T & string;
4};
5interface DynamicPlayerstableProps<T> {
6  columns: Array<TableColumn<T>>;
7  data: Array<T>;
8}

That resolves that issue but introduces another one where typescipt doesn't know what type T is and what type T[keyof T] is going to resolve to

Because in it's current shape bothe

tsx

1type Player = {
2  id: number;
3  name: string;
4  age: number;
5  rank: string;
6};
7//  and
8
9type playeyWithArrays = {
10  id: Array<number>;
11  name: Array<string>;
12  age: Array<number>;
13  rank: Date;
14  ratio: {
15    numerator: number;
16    denominator: number;
17  };
18};

>[!TIP]

any type can be passed into the component as type T , react and our table doesn't expect that and will throw an error if we try to render an array or Date object in a td or any react node . so to further specify what inputs we expect we can use the extends operator

>[!NOTE]

in typescript it's either used to inherit behaviour from a class or to mark a generic type as a subtype of another more specific type

tsx

1T extends string // can only accept strings
2T extends {} // can only accept objects
3T extends {id:number} // can only accept objects with a key `id` that is a number
4T extends Record<string, string | number> // can only accept objects with string or number keys

We'll use this to specify that only objects with string or number keys can be passed into the table

>[!NOTE]

Record<TKey, TValue> can be used to specify objects

tsx

1type TableColumn<T extends Record<string, string|number >> = {
2  label: string;
3  accessor: keyof T & string;
4};
5interface GenericTableProps<T extends Record<string, string|number >> {
6  columns: Array<TableColumn<T>>;
7  data: Array<T>;
8}
9
10export function GenericTable<T extends Record<string, string|number >>

now with this we can only pass in objects that have string or number keys

tsx

1const data = [
2  {
3    id: 1,
4    name: "John Doe",
5    age: 30,
6    rank: "Gold",
7  },
8];
9const baddata = [
10  {
11    id: 1,
12    name: "John Doe",
13    age: [30],
14    rank: new Date(),
15  },
16];

before restrictions ![bad inputs without restriction](https://github.com/tigawanna/ReactDevsKe-Meetup-February-2025/raw/d45806eca0a9a6b67f047b439894905a0b712450/docs/before-restriction.png) after restrictions ![bad inputs with restriction](https://github.com/tigawanna/ReactDevsKe-Meetup-February-2025/raw/d45806eca0a9a6b67f047b439894905a0b712450/docs/after-enforcement.png)

one last thing is rqeire type T to include a key id because it's going to be used as the key for the table rows

tsx

1type GenericItem = Record<string, string | number> & { id: string }; // field of id:string required in passed in objects
2type TableColumn<T extends GenericItem> = {
3  label: string;
4  accessor: keyof T & string;
5};
6interface GenericTableProps<T extends GenericItem> {
7  columns: Array<TableColumn<T>>;
8  data: Array<T>;
9}
10
11export function GenericPlayerstable<T extends GenericItem>({ data, columns }: GenericTableProps<T>);

T-with-no-id

>[!TIP] >Bonus tip : handling nested objects

tsx

1const data = [
2  {
3    id: "1",
4    name: "John Doe",
5    age: 30,
6    rank: "Gold",
7    ratio: {
8      numerator: 1,
9      denominator: 2,
10    },
11  },
12];

This type will cause issues because field ratio is an object and we can't render it directly in the table because react can't render objects as its children

First the Record type should also intersect with an object type

tsx

1// now lets the value of the record to be an object
2type GenericItem = Record<string, string | number | object> & { id: string };
3type TableColumn<T extends GenericItem> = {
4  label: string;
5  accessor: PossibleNestedUnions<T, 10> & string;
6};
7
8interface GenericTableProps<T extends GenericItem> {
9  title:string;
10  description?:string;
11  columns: Array<TableColumn<T>>;
12  data: Array<T>;
13}

Then we add checks to handle object types

tsx

1          <tbody>
2            {data.map((row) => (
3              <tr key={row.id}>
4                {columns.map((column) => {
5                  const value = row[column.accessor];
6                  // this line grabs the nested object and maps it to a <td>
7                  if (column.accessor.includes(".")) {
8                    return <td key={column.accessor}>{getNestedProperty(row, column.accessor)}</td>;
9                  }
10                  //  we've already checked if the accessor is a nested object but typescript is not yet aware and 
11                  // still thinks value is type string | number | objct at this point 
12                  //  this part is only here to narrow the type or catch objects types that fell through
13                  //  so that the value type on the section below is of type string | number
14                  if (typeof value === "object") {
15                    const nestedValue = getNestedProperty(row, column.accessor)
16                    if(typeof nestedValue !== "string" || typeof nestedValue !== "number") {
17                      // to avoid accidentally trying to renedr objects as react children
18                      return <td key={column.accessor}>{JSON.stringify(nestedValue)}</td>;
19                    }
20                    return <td key={column.accessor}>{getNestedProperty(row, column.accessor)}</td>;
21                  }
22                  // value type is string| number , safe to render ina react td 
23                  return <td key={column.accessor}>{value}</td>;
24                })}
25              </tr>
26            ))}
27          </tbody>

getNestedProperty is a utility function to retrieve a nested property value from an object based on a dot-separated path

example

tsx

1const obj = { a: { b: { c: 42 } } };
2console.log(getNestedProperty(obj, "a"));   // Outputs: { b: { c: 42 } }
3console.log(getNestedProperty(obj, "a.b.c")); // Outputs: 42
4console.log(getNestedProperty(obj, "a.b.x")); // Outputs: undefined

so how do we get the types to the dot separated values? this one is non trivial and one of the examples of the ugly typescript people hate. PossibleNestedUnions uses recursion to extract the dot separated keys to inputs of type nested object

example

typescript

1type ExampleType = {
2  a: string;
3  b: {
4    c: number;
5    d: {
6      e: boolean;
7      f: {
8        g: string;
9      };
10    };
11  };
12  h: Date;
13};
14
15type NestedKeys1 = PossibleNestedUnions<ExampleType, 1>;  // "a" | "b" | "h"
16type NestedKeys2 = PossibleNestedUnions<ExampleType, 2>;  // "a" | "b" | "b.c" | "b.d" | "h"
17type NestedKeys3 = PossibleNestedUnions<ExampleType, 3>;  // "a" | "b" | "b.c" | "b.d" | "b.d.e" | "b.d.f" | "h"
18type NestedKeysAll = PossibleNestedUnions<ExampleType>;   // includes all nested paths

and now our new type will be

tsx

1import { PossibleNestedUnions } from "../types/nested_objects_union";
2import { getNestedProperty } from "../utils/object";
3
4type GenericItem = Record<string, string | number | object>&{id:string}
5type TableColumn<T extends GenericItem> = {
6  label: string;
7  accessor: PossibleNestedUnions<T> & string;
8};
9interface GenericTableProps<T extends GenericItem> {
10  columns: Array<TableColumn<T>>;
11  data: Array<T>;
12}

with the array

typescript

1   const gooddata = [
2     {
3       id: "1",
4       name: "John Doe",
5       age: 30,
6       rank: "Gold",
7       stats:{
8        running:20,
9        jumping:10,
10        swimming:30,
11        weapons:{
12          stars:10,
13          katana:5
14        }
15       }
16     },
17     {
18       id: "2",
19       name: "Pedro",
20       age: 30,
21       rank: "Gold",
22       stats:{
23        running:20,
24        jumping:10,
25        swimming:30,
26        weapons:{
27          stars:1,
28          katana:4,
29          blades:{
30            short:10,
31            long:5
32          }
33        }
34       }
35     },
36   ];

we'll get auto complete for all the possibly nested types ![netsed-values-auto comlete](https://github.com/tigawanna/ReactDevsKe-Meetup-February-2025/raw/main/docs/netsed-values-auto%20comlete.png)

Finally we can make the title and description of the table dynamic too because we can render more than just players with this component

tsx

1      <GenericTableWithNestedFields
2      title="Players Table"
3        description="list of players without their stats"
4        data={gooddata}
5        columns={[
6          { accessor: "id", label: "age" },
7          { accessor: "name", label: "name" },
8          { accessor: "age", label: "age" },
9          { accessor: "rank", label: "rank" },
10        ]}
11      />
12      <GenericTableWithNestedFields
13      title="Players Table with stats"
14        description="list of players with their stats"
15        data={gooddata}
16        columns={[
17          { accessor: "id", label: "age" },
18          { accessor: "name", label: "name" },
19          { accessor: "age", label: "age" },
20          { accessor: "rank", label: "rank" },
21          { accessor: "stats.running", label: "running" },
22          { accessor: "stats.jumping", label: "jumping" },
23          { accessor: "stats.swimming", label: "swimming" },
24          { accessor: "stats.weapons.blades.short", label: "katana" },
25        ]}
26      />

publishing to npm

Publishing to npm requires 3 things

a nodejs project
a package.json file . an npm account

in our case we also need

tsconfig for typescript
tsup for transpiling (we could use tsc for this too)

create a node project

bash

1npm init -y
2npm install typescript --save-dev
3tsc --init

we'll change the tsconfig to look like this source + explanation

json

1{
2  "compilerOptions": {
3    /* Base Options: */
4    "esModuleInterop": true,
5    "skipLibCheck": true,
6    "target": "es2022",
7    "allowJs": true,
8    "resolveJsonModule": true,
9    "moduleDetection": "force",
10    "isolatedModules": true,
11    "verbatimModuleSyntax": true,
12
13    /* Strictness */
14    "strict": true,
15    "noUncheckedIndexedAccess": true,
16    "noImplicitOverride": true,
17
18    /* If transpiling with TypeScript: */
19    // "module": "NodeNext",
20    "outDir": "dist",
21    // "sourceMap": true,
22
23    /* AND if you're building for a library: */
24    "declaration": true,
25
26    /* AND if you're building for a library in a monorepo: */
27    // "composite": true,
28    // "declarationMap": true,
29
30    /* If NOT transpiling with TypeScript: */
31    "module": "preserve",
32    "noEmit": true,
33    /* If your code doesn't run in the DOM: */
34    // "lib": ["es2022"]
35    /* If your code runs in the DOM: */
36    "lib": ["es2022", "dom", "dom.iterable"],
37    // if you want to use JSX (react)
38    "jsx":"react-jsx",
39
40    "paths": {
41      "@/*": ["./src/*"]
42    },
43    
44  },
45  // only files under `src` will be transpiled
46  "include": ["src"],
47  // exclude files under `dist` and `node_modules`
48  "exclude": ["dist", "node_modules"]
49}

Our file will be in the src directory with an index.ts file as the main entrypoint

>[!NOTE]

Entrypoint is the file that is executed when the package is imported

example

typescript

1// my-table-package is the name of the package which is the default entrypoint
2import { GenericTable } from "my-table-package";

entry points are defined in the package.json file

json

1{
2  "name": "my-table-package",
3  "version": "1.0.0",
4  "type": "module",
5  // our transipiled file will be in the `dist` directory
6  "files": [
7    "dist"
8  ],
9  // our entrypoint is the `index.ts` file
10  "main": "dist/index.js",
11  // the exports field is a newer syntax for node 16+ that allows for multiple entrypoints
12  "exports": {
13    ".": {
14      "import": "./dist/index.js",
15      "require": "./dist/index.cjs"
16    },
17    // we can also define exports for specific files
18    "/styles":"./dist/index.css"
19  },
20  // peer dependencies are dependencies that we expect the user of the package to already have installed , if we're unsure that thy'll have it we put it i the dependencies field (it might lead to bigger final size)
21    "peerDependencies": {
22    "react": "^18.0.0 || ^19.0.0",
23    "react-dom": "^18.0.0 || ^19.0.0",
24    "tailwindcss": "^3.0.0 || ^4.0.0",
25    "daisyui": " ^4.0.0 || ^5.0.0-beta"
26  },
27  // devDependencies are dependencies that are only used for development and don't get included in the final package
28  // if uo have peer dependencies u can put them in dev dependencies
29  "devDependencies": {
30    "@arethetypeswrong/cli": "^0.17.3",
31    "@changesets/cli": "^2.27.12",
32    "@eslint/js": "^9.19.0",
33    "@types/node": "^22.12.0",
34    "@types/react": "^19.0.8",
35    "daisyui": "5.0.0-beta.6",
36    "eslint": "^9.19.0",
37    "prettier": "^3.4.2",
38    "react": "^19.0.0",
39    "tailwindcss": "^4.0.1",
40    "tsup": "^8.3.6",
41    "typescript": "^5.7.3"
42  }
43}

We'll build this package using tsup . we can use tsc (the typescript compiler) to build the package but that would require some changes

```json
//tsconfig.json
{
/* If transpiling with TypeScript: */
"module": "NodeNext",
"sourceMap": true,
}

typescript

1
2which requires that all our import should end with the file extension name 
3

ts import { GenericTable } from "./src/components/GenericTable"; // to be import { GenericTable } from "./src/components/GenericTable.js";

typescript

1which can be a bit much if we already have the code we want to publish
2to use tsup we just add a config 
3

ts //tsup.config.ts import { defineConfig } from "tsup";

export default defineConfig({ entry: ["src/index.ts","src/components/RedSquare.tsx"], splitting: false, format: ["cjs", "esm"], dts: true, clean: true, minify: false, platform: "browser", });

typescript

1 and with our build script
2

json { "scripts": { "dev": "tsup --watch", "build": "tsup", "format": "prettier --write .", "typecheck": "tsc", "lint": "eslint --quiet .", "ci:version": "changeset version", "ci:release": "changeset publish", "release": "changeset publish --no-git-checks", "check-exports": "attw --pack . --ignore-rules=cjs-resolves-to-esm --profile node16" } }

sh npm run build

typescript

1
2the outputs should be in the `dist` directory
3and tio test if our component works (am using pnpm)
4we check the working directory using `pwd` then head to the project we want to install the package in and run
5

sh pnpm install <file-path-to-package>

typescript

1which adds a linked package like this 
2

json "dependencies": { "@tailwindcss/vite": "^4.0.1", //locally linked package "my-table-package": "link:/home/dennis/Desktop/packaging/my-table-package", "pp": "^1.0.0", "react": "^19.0.0", "react-dom": "^19.0.0", "tailwindcss": "^4.0.1" }

typescript

1
2>[!NOTE] 
3if u're not using pnpm u can use `npm link` instead of `pnpm install`
4
5>[!WARNING] 
6This will only work if you build yoour project locally where the package project also is , if you ad this to a projecct that get's build in CI or any other machnie it will not work
7
8to make it usable by everyone we publish it to npm using

sh npm publish

typescript

1
2>[!NOTE]
3 once at least one project installs your library it will be 
4 undeletable from the npm registry
5
6### Extras
7- check exports with [are the types correct](https://github.com/arethetypeswrong/arethetypeswrong.github.io#readme)
8to chek if everything is being exported correctly
9

json { "scripts": { "dev": "tsup --watch", "build": "tsup", "format": "prettier --write .", "typecheck": "tsc", "lint": "eslint --quiet .", "ci:version": "changeset version", "ci:release": "changeset publish", "release": "changeset publish --no-git-checks", "check-exports": "attw --pack . --ignore-rules=cjs-resolves-to-esm --profile node16" } }

sh npm run check-exports

typescript

1
2- [create a changelog](https://blog.logrocket.com/automatically-generate-and-release-a-changelog-with-node-js/)
3- write unit tests
4- use other entrypoint , useful for
5   
6  - optimize and minimize the bundle size by allowing tree-shaking
7  - separate and organize code into logical modules for better maintainability
8  - enable independent development and testing of different components
9  - facilitate conditional loading of features based on environment or user preferences
10  - improve application startup time by loading only necessary code
11  - enhance code reuse across different parts of the application or projects
12
13example

ts // /src/inde: main entrypoint contents

import { GenericTable } from "./components/GenericTable"; import { GenericTableWithNestedFields } from "./components/GenericTableWithNestedFields"; import { HardCodedTable } from "./components/HardCodedTable";

export { GenericTable, GenericTableWithNestedFields, HardCodedTable };

ts import { defineConfig } from "tsup";

export default defineConfig({ // our entrypoint is the index.ts file // RedSquare.tsx component will be build with it's own entrypoint entry: ["src/index.ts","src/components/RedSquare.tsx"], splitting: false, format: ["cjs", "esm"], dts: true, clean: true, minify: false, platform: "browser",

});

json { "exports": { // default entrypoint
".": { "import": "./dist/index.js", "require": "./dist/index.cjs" }, // /redbox entrypoint "./redbox": "./dist/components/RedSquare.js" }, }

ts // import the default entrypoint import { GenericTable } from "my-table-package"; // import the redbox entrypoint import { RedBox} from "my-table-package/redbox";
```

The end