1
00:00:00,320 --> 00:00:05,210
Flags in regular expressions modify
the way the expression behaves.

2
00:00:05,210 --> 00:00:09,070
There are a number of flags,
but we'll focus on three.

3
00:00:09,070 --> 00:00:14,280
Each one of these flags overrides
a default behavior of regular expressions.

4
00:00:14,280 --> 00:00:18,050
First, i stands for case-insensitive.

5
00:00:18,050 --> 00:00:23,010
Using i will make the parser disregard
case when searching for matches.

6
00:00:23,010 --> 00:00:24,720
G is for global.

7
00:00:24,720 --> 00:00:29,500
By default, the regular expression will
stop searching once it finds a match.

8
00:00:29,500 --> 00:00:34,070
The g flag tells the parser to find
all matches contained in a string.

9
00:00:34,070 --> 00:00:36,948
The m flag stands for multiline.

10
00:00:36,948 --> 00:00:41,195
Normally a caret will only match
the very beginning of a string and

11
00:00:41,195 --> 00:00:44,010
a dollar sign will only match the end.

12
00:00:44,010 --> 00:00:48,780
Any line breaks the string contains
will be considered part of the string.

13
00:00:48,780 --> 00:00:53,850
Setting the m flag will cause the parser
to treat line breaks like new lines.

14
00:00:53,850 --> 00:00:57,160
A caret will match the beginning
of each new line and

15
00:00:57,160 --> 00:00:59,000
a dollar sign will match the end.

16
00:00:59,000 --> 00:01:03,770
To add any of these flags
to a regex in JavaScript,

17
00:01:03,770 --> 00:01:07,250
put them after the last
slash of a regex literal.

18
00:01:07,250 --> 00:01:08,640
You can put them in any order.

19
00:01:09,790 --> 00:01:11,330
Let's see these in use.

20
00:01:11,330 --> 00:01:16,940
I'm still in my console,
I'll create a new string LION

21
00:01:16,940 --> 00:01:19,820
in all caps and call replace on it.

22
00:01:20,850 --> 00:01:26,530
I'll pass a regex matching lion in
lowercase and add the i flag to it.

23
00:01:28,440 --> 00:01:31,503
And let's make
the replacement string mouse.

24
00:01:33,341 --> 00:01:35,914
You can see LION was replaced.

25
00:01:35,914 --> 00:01:40,002
Note, you could also use
a character set containing a to z.

26
00:01:44,190 --> 00:01:46,665
All lowercase.

27
00:01:46,665 --> 00:01:48,750
Let's use the global flag.

28
00:01:48,750 --> 00:01:50,430
I'll use a slightly different string.

29
00:01:50,430 --> 00:01:55,138
I'll clear my console and type,

30
00:01:55,138 --> 00:02:00,526
she ate watermelon at the waterpark.

31
00:02:03,304 --> 00:02:06,407
I'll look for water and
replace it with an empty string.

32
00:02:12,008 --> 00:02:15,500
In other words,
I want to delete the string, water.

33
00:02:15,500 --> 00:02:19,600
Notice how the parser found and
replaced the first occurrence of water and

34
00:02:19,600 --> 00:02:21,670
left the second one alone.

35
00:02:21,670 --> 00:02:26,410
If we wanted the parser to replace all
occurrences, we could add a g flag.

36
00:02:28,510 --> 00:02:31,620
Now both occurrences of
the name have been replaced.

37
00:02:31,620 --> 00:02:34,520
If there were more,
they would have been replaced too.

38
00:02:34,520 --> 00:02:38,961
Now I'll create a variable called treat
and I'll store a multiline string in it.

39
00:02:41,805 --> 00:02:44,583
Each line of the string
is the word cheese.

40
00:02:49,242 --> 00:02:54,992
Now I'll call replace on it and
pass in the regular expression

41
00:02:54,992 --> 00:03:00,088
matching a string that only
contains the word cheese.

42
00:03:04,115 --> 00:03:05,520
I'll replace it with fruit.

43
00:03:08,382 --> 00:03:11,910
The regex doesn't match it because
the string contains the word

44
00:03:11,910 --> 00:03:15,040
cheese three times with new lines.

45
00:03:15,040 --> 00:03:19,280
If I add the m flag,

46
00:03:19,280 --> 00:03:23,570
you can see that the first instance
of cheese was changed to fruit.

47
00:03:23,570 --> 00:03:25,400
The parser found the line break and

48
00:03:25,400 --> 00:03:28,710
considered the first
instance of cheese to match.

49
00:03:28,710 --> 00:03:32,755
The other instances were not matched
because we didn't set the global flag.

50
00:03:33,930 --> 00:03:35,651
I'll put a g now.

51
00:03:37,489 --> 00:03:40,530
All of the instances of
cheese are turned to fruit.

52
00:03:40,530 --> 00:03:44,000
You'll see flags often in
other regular expressions and

53
00:03:44,000 --> 00:03:45,710
it's good to know about them.

54
00:03:45,710 --> 00:03:50,850
Later in the course for example, we'll
make use of the case-insensitive flag.

55
00:03:50,850 --> 00:03:55,658
I'd probably use the global flag most of
all to replace occurrences of a name, for

56
00:03:55,658 --> 00:03:58,120
example, or to delete blank lines.

57
00:03:59,750 --> 00:04:04,790
You're ready to start adding validation
to the form I showed in an earlier video.

58
00:04:04,790 --> 00:04:08,450
In the next video, I'll show you
the code we'll be starting with.

59
00:04:08,450 --> 00:04:11,530
Then, we'll validate the user name input.

60
00:04:11,530 --> 00:04:12,350
Let's get started.