1 · Structure and rendering · 30 MIN

Files, paths and resource boundaries

File access should use a deliberate base path and explicit encoding.

The filesystem promises API provides asynchronous operations. A file URL resolved against import.meta.url locates a resource relative to the module rather than whichever directory launched the process. This example writes only inside a new temporary directory and cleans it up in finally. A real endpoint must not pass an arbitrary user path directly to readFile: input paths can escape the intended directory. readFile buffers the entire file, so use streaming for large inputs.

Run from a different working directory.

Read the example

import {mkdtemp,writeFile,readFile,rm} from 'node:fs/promises';
import {tmpdir} from 'node:os';
import {join} from 'node:path';
const dir=await mkdtemp(join(tmpdir(),'codingneed-lesson-'));
try {
  const file=join(dir,'notes.txt');
  await writeFile(file,'Learn paths safely.','utf8');
  console.log(await readFile(file,'utf8'));
} finally {await rm(dir,{recursive:true,force:true})}

Learn paths safely. The newly created temporary directory is removed afterwards.

Your challenge

Add a missing-file case and handle only ENOENT as an expected absence; preserve other errors.

Solution cost: O(b) file I/O for b bytes. time · O(b) readFile buffering. space

Common trap

Catching every file error as not found hides permission and disk failures.

import {mkdtemp,writeFile,readFile,rm} from 'node:fs/promises';
import {tmpdir} from 'node:os';
import {join} from 'node:path';
const dir=await mkdtemp(join(tmpdir(),'codingneed-lesson-'));
try {
  const file=join(dir,'notes.txt');
  await writeFile(file,'Learn paths safely.','utf8');
  console.log(await readFile(file,'utf8'));
} finally {await rm(dir,{recursive:true,force:true})}

Further reading: Official documentation