# The easiest way to set up absolute paths in your TypeScript Node.js project

### Step-by-step guide. Works with Nest.js or any other Node.js project. I'm going to show you how to do this quickly and easily, so let's get started.

<br/>

## Configure absolute paths

1. Initialize the new package in the terminal if you haven't already done so:

```zsh
npm init -y

yarn init -y
```

Your package.json should look something like this:

```json
{
    "name": "absolute-paths",
    "version": "1.0.0",
    "main": "index.js",
    "license": "MIT"
}
```

<br/>

2. Similarly with tsconfig:

```zsh
npx tsc --init
```

And don't forget to install typescript as devDependency:

```zsh
npm i -D typescript @types/node

yarn add -D typescript @types/node
```

<br/>

3. Now let's install the necessary dependencies:

```zsh
npm i -D ts-node ts-patch tsc-alias tsconfig-paths typescript-transform-paths

yarn add -D ts-node ts-patch tsc-alias tsconfig-paths typescript-transform-paths
```

<br/>

4. Next, you need to customize tsconfig.json a bit:

```js
// tsconfig.json

{
    "compilerOptions": {
        ...,
        "baseUrl": "src" /* Specify the base directory to resolve non-relative module names. */,
        "paths": {
            "@/*": ["*"]
        } /* Specify a set of entries that re-map imports to additional lookup locations. */,

        "plugins": [
            /* Transform paths in output .js files */
            {
                "transform": "typescript-transform-paths"
            },
            /* Transform paths in output .d.ts files */
            {
                "transform": "typescript-transform-paths",
                "afterDeclarations": true
            }
        ],
        ...
    }
}
```

<br/>

5. After that, add a few scripts to the package.json file:

```js
// package.json

{
    ...,
     "scripts": {
        "ts-prepare": "ts-patch install -s",
        "start:dev": "yarn ts-prepare && ts-node ./src/index.ts",
        "start:prod": "node ./build/index.js",
        "build": "tsc && tsc-alias"
    },
    ...
}
```

Before running the code in development mode, you need to run the `ts-prepare` command, and for a successful build, after it, run `tsc-alias`

<br/>

6. That's it! You can now use absolute paths in your project. You can also see some code examples below.

<br/>

## Code example

Project file structure

```
├── package.json
├── src
│   ├── dir
│   │   └── file.ts
│   └── index.ts
└── tsconfig.json
```

`package.json`

```json
{
    "name": "absolute-paths",
    "version": "1.0.0",
    "main": "index.js",
    "license": "MIT",
    "scripts": {
        "ts-prepare": "ts-patch install -s",
        "start:dev": "npm run ts-prepare && ts-node ./src/index.ts",
        // or
        "start:dev": "yarn ts-prepare && ts-node ./src/index.ts",
        "start:prod": "node ./build/index.js",
        "build": "tsc && tsc-alias"
    },
    "devDependencies": {
        "@types/node": "^20.5.0",
        "ts-node": "^10.9.1",
        "ts-patch": "^3.0.2",
        "tsc-alias": "^1.8.7",
        "tsconfig-paths": "^4.2.0",
        "typescript": "^5.1.6",
        "typescript-transform-paths": "^3.4.6"
    }
}
```

`tsconfig.json`

```js
{
    "compilerOptions": {
        "target": "es2017" /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */,
        "module": "commonjs" /* Specify what module code is generated. */,
        "outDir": "build" /* Specify an output folder for all emitted files. */,
        "strict": true /* Enable all strict type-checking options. */,
        "skipLibCheck": true /* Skip type checking all .d.ts files. */,

        /* IMPORTANT */

        "baseUrl": "src" /* Specify the base directory to resolve non-relative module names. */,
        "paths": {
            "@/*": ["*"]
        } /* Specify a set of entries that re-map imports to additional lookup locations. */,

        "plugins": [
            /* Transform paths in output .js files */
            {
                "transform": "typescript-transform-paths"
            },
            /* Transform paths in output .d.ts files */
            {
                "transform": "typescript-transform-paths",
                "afterDeclarations": true
            }
        ]

        /* End of IMPORTANT */
    },
    "ts-node": {
        "transpileOnly": true,
        "files": true
    },
    "include": ["src/**/*"],
    "exclude": ["node_modules", "build"]
}
```

`/src/index.ts`

```ts
import { someData } from '@/dir/file'

console.log(someData)
```

`/src/dir/file.ts`

```ts
export const someData = 'some data'
```

Run the code

```zsh
npm run start:dev

yarn start:dev
```

Output

`npm`

```zsh
absolute-paths $ npm run start:dev

> absolute-paths@1.0.0 start:dev
> npm run ts-prepare && ts-node ./src/index.ts


> absolute-paths@1.0.0 ts-prepare
> ts-patch install -s

some data
```

`yarn`

```zsh
absolute-paths $ yarn start:dev
$ yarn ts-prepare && ts-node ./src/index.ts
$ ts-patch install -s

some data

✨  Done.
```