Gulp: Why doesn't a file have an extname property in stream?

Question

Node.js

I watch screencasts by I. Kantor on Gulp. Why don't I have it in the screencast, in the stream, the file doesn't have an extname?
Here is gulpfile.js code:

'use strict';

var gulp = require('gulp');

gulp.task('default', function() {
  return gulp.src('source/**/*.*').
    on('data', function(file) {
      console.dir(file.extname);
    })
});

and here is the output in the console:
[23:09:37] Using gulpfile ~\Desktop\gulp\project\gulpfile.js
[23:09:37] Starting 'default'...
undefined
undefined
[23:09:37] Finished 'default' after
22 ms

gulp.task('default', function() {
  return gulp.src('source/**/*.*').pipe(gulp.dest(function(file) {
    console.dir(file.extname);
    return 'dest';
  }));
});

and this is what the console outputs:
[23:22:01] Using gulpfile ~\Desktop\gulp\project\gulpfile.js
[23:22:01] Starting 'default'...
File {
history: [ 'C:\\ Users\\rain-\\Desktop\\gulp\\project\\source\\1\\1.css' ],
cwd: 'C:\\Users\\rain-\\Desktop\\gulp\\project' ,
base: 'C:\\Users\\rain-\\Desktop\\gulp\\project\\source\\',
stat:
{ dev: -2041281915,
mode: 33206,
nlink: 1,
uid: 0,
gid : 0,
rdev: 0,
blksize: undefined,
ino: 2251799813836494,
size: 36,
blocks: undefined,
atime: 2016-10-08T19:30:35.000Z,
mtime: 2016-10-08T19:45:27.000Z,
ctime: 2016-10-08T19:45:27.665Z,
birthtime: 2016-10-08T19:30:35.357Z },
_contents:
Buffer [
98,
111,
100,
121,
32,
123,
13,
10,
32,
32 ,
98,
97,
99,
107,
103,
114,
111,
117,
110,
100,
45,
99,
111,
108,
111,
114,
58,
32,
35,
102,
102,
102,
59,
13,
10,
125 ] }
File {
history: [ 'C:\\Users\\rain-\\Desktop\\gulp\\project\\source\\1\\1.js' ],
cwd : 'C:\\Users\\rain-\\Desktop\\gulp\\project',
base: 'C:\\Users\\rain-\\Desktop\\gulp\\project\\source\\',
stat:
{ dev: -2041281915,
mode: 33206,
nlink: 1,
uid: 0,
gid: 0,
rdev: 0,
blksize: undefined,
ino: 3940649674100336,
size: 18,
blocks: undefined,
atime: 2016-10- 08T19:30:03.000Z,
mtime: 2016-10-08T19:45:29.000Z,
ctime: 2016-10-08T19:45:29.373Z,
birthtime: 2016-10-08T19:30:03.568Z },
_contents:
Buffer [
118,
97,
114,
32,
110,
97,
109,
101,
32,
61,
32,
39,
77,
105,
107,
101,
39,
59 ] }
[23:22:01] Finished 'default' after 52 ms
That is, file has only 5 properties, these are history, cwd, base, stat and Buffer. Properties realative, extname does not even smell.
Why don't I have this? Ilya has it in the screencast. Maybe because of the version? He put the fourth version, I'll help you with 3.9.1.
What's wrong?

Answer 1

gulp.task('default', function() {
  return gulp.src('source/**/*.*').pipe(gulp.dest(function(file) {
    console.log(file.extname);
    return 'dest';
  }));
});