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Regular Expressions in JavaScript

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Beginning and Ending of Strings

2:01 with Joel Kraft

It's important to be able to specify that a regular expression starts matching at the beginning of a string and match all the way to the end. Learn more in this video.

RegexPal

Since the recording of this video RegexPal updated their UI. You can adjust the flags just above the input where you enter your regex. To follow along with this video you'll want to make sure that both the global and multiline flags are selected.

Practice

Copy both the Match and the Exclude set of test strings from each exercise below into a Regex tester like RegEx Pal or regex101. Using what you've learned so far, create a regular expression that will match all of the strings in the Match set and exclude the ones in the Exclude set.

1 )
Match:
tart
Exclude:
start
tartan

2 )
Match:
img_01.jpg
img_02.png
img_03.gif
img_04.png
img_05.gif
img_06.jpg
Exclude:
6_img_07.gif
mov_01.avi

3 )
Match:
projector
protractor
projected
Exclude:
proctor
my projector
projecting
projectorlight

4 )
Match:
3456
34567
Exclude:
23456
345678

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    Notice this string I typed in the last video, wwwgoogle.com. 0:00
    Even though we've grouped the www dot together, 0:06
    the regex is still finding a partial match in this test string. 0:09
    As you can see, it does this by starting to match the pattern, 0:14
    later in the string, at the fourth character. 0:18
    We can see the opposite problem by typing another test string, 0:20
    with extra characters at the end. 0:24
    If we're trying to match Google.com, neither of these strings are valid. 0:28
    We can tell the parser to only consider these a match if the entire string 0:33
    fits our pattern, and to reject partial matches like these. 0:37
    You will see these characters often in regex's. 0:42
    They are very useful in ensuring, 0:45
    you are only matching at the beginning or ending of a string. 0:47
    While other regex characters have represented characters and 0:51
    strings, these only represent location. 0:54
    As I mentioned in the first video, 0:59
    make sure you have this checked, match at line breaks. 1:01
    This lets us treat each line as a separate test string rather than one block. 1:05
    To tell the parser to only start matching at the beginning of test strings 1:10
    I'll put a caret at the beginning of the regex. 1:15
    You see, that excluded wwwgoogle.com because 1:19
    if www is present, it must be followed by a dot. 1:24
    Now to specify the string must end with net or 1:29
    com, with only one m, I'll put a dollar sign at the end of the expression. 1:32
    Now all of the valid strings are matched. 1:38
    You'll probably use a carat and dollar sign often in your regular expressions to 1:41
    eliminate strings that contain the pattern you're matching, but 1:46
    as a whole would be considered invalid. 1:49
    Find some additional practice in the teacher's notes below. 1:53
    Next, let's start using everything we've learned in a real project. 1:56

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