Filesystem Access
Many introductory programming books cover filesystem access because it’s considered
a critical part of “normal” programming. Poor JavaScript: up until Node, it wasn’t in
the filesystem club.
The examples in this chapter assume your project root is /home/<jdoe>/fs, which is a
typical path on a Unix system (replace <jdoe> with your username). The same princi‐
ples apply on a Windows system (where your project root might be C:\Users\<John
Doe>\Documents\fs).
To create a file, use
fs.writeFile
. Create a file in your project root called write.js:
const
fs
=
require
(
'fs'
);
fs
.
writeFile
(
'hello.txt'
,
'hello from Node!'
,
function
(
err
) {
if
(
err
)
return
console
.
log
(
'Error writing to file.'
);
});
This will create a file in the directory you’re in when you run write.js (assuming you
have sufficient privileges in that directory, and there isn’t a directory or read-only file
called hello.txt already). Whenever you invoke a Node application, it inherits its cur‐
rent working directory from where you run it from (which may be different than
where the file lives). For example:
$ cd /home/jdoe/fs
$ node write.js # current working dir is /home/jdoe/fs
# creates /home/jdoe/fs/hello.txt
$ cd .. # current working dir is now /home/jdoe
$ node fs/write.js # creates /home/jdoe/hello.txt
Node provides a special variable,
__dirname
, which is always set to the directory in
which the source file resides. For example, we can change our example to:
const
fs
=
require
(
'fs'
);
fs
.
writeFile
(
__dirname
+
'/hello.txt'
,
'hello from Node!'
,
function
(
err
) {
if
(
err
)
return
console
.
error
(
'Error writing to file.'
);
});
Now write.js will always create hello.txt in /home/<jdoe>/fs (where write.js is located).
Using string concatenation to join
__dirname
and our filename isn’t very platform-
agnostic; this could cause problems on a Windows machine, for example. Node pro‐
vides platform-independent pathname utilities in the module
path
, so we can rewrite
this module to be more friendly on all platforms:
const
fs
=
require
(
'fs'
);
const
path
=
require
(
'path'
);
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