function ftruncate
Usage in Deno
```typescript import { ftruncate } from "node:node__fs.d.ts"; ```
ftruncate(): void
Truncates the file descriptor. No arguments other than a possible exception are
given to the completion callback.
See the POSIX [`ftruncate(2)`](http://man7.org/linux/man-pages/man2/ftruncate.2.html) documentation for more detail.
If the file referred to by the file descriptor was larger than `len` bytes, only
the first `len` bytes will be retained in the file.
For example, the following program retains only the first four bytes of the
file:
```js
import { open, close, ftruncate } from 'node:fs';
function closeFd(fd) {
close(fd, (err) => {
if (err) throw err;
});
}
open('temp.txt', 'r+', (err, fd) => {
if (err) throw err;
try {
ftruncate(fd, 4, (err) => {
closeFd(fd);
if (err) throw err;
});
} catch (err) {
closeFd(fd);
if (err) throw err;
}
});
```
If the file previously was shorter than `len` bytes, it is extended, and the
extended part is filled with null bytes (`'\0'`):
If `len` is negative then `0` will be used.
void
ftruncate(fd: number,callback: NoParamCallback,): void
Asynchronous ftruncate(2) - Truncate a file to a specified length.
callback: NoParamCallback
void