In-Memory Filesystem Repository for Node.js & TypeScript

fs-fake.ts

import * as fs from "node:fs/promises";

type Disk = Map<string, string>;

interface FileSystemAdapter {
    readFile(path: string): Promise<string>;
    writeFile(path: string, content: string): Promise<void>;
    deleteFile(path: string): Promise<void>;
}

class InMemoryFileSystem implements FileSystemAdapter {
    private readonly disk: Disk;

    constructor(disk?: Disk) {
        this.disk = disk ?? new Map();
    }

    public async readFile(path: string): Promise<string> {
        const contents = this.disk.get(path);

        if (!contents) {
            throw new Error(`File ${path} not found or not readable`);
        }

        return contents;
    }

    public async writeFile(path: string, content: string): Promise<void> {
        this.disk.set(path, content);
    }

    public async deleteFile(path: string): Promise<void> {
        this.disk.delete(path);
    }
}

class RealFileSystem implements FileSystemAdapter {
    private readonly encoding: 'utf8' = 'utf8';

    public async readFile(path: string): Promise<string> {
        return fs.readFile(path, { encoding: this.encoding });
    }

    public async writeFile(path: string, content: string): Promise<void> {
        fs.writeFile(path, content, { encoding: this.encoding });
    }

    public async deleteFile(path: string): Promise<void> {
        fs.unlink(path);
    }
}