JS regexp

/pattern/[switches]

1. Meta chars vs literals
2. Character classes [..]
    [abc]   Character class, any character from a set of characters
    [^abc]  Inverted char class, any character not in a set of characters
    [0-9] or [a-zA-Z] Any character in a range of characters
3. Quantifiers:
    x+  One or more occurrences of the pattern x
    x?  Zero or one occurrence
    x*  Zero or more occurrences
    x+? One or more occurrences, non-greedy
    x{n}    Interval quantifier, matches exactly n times
    x{n,}   At least n times
    x{n,m}  Between n and m occurrences

4. backreferencing
    \n - A back reference to the last substring matching the n parenthetical
         in the regular expression (counting left parentheses).
    For example, /apple(,)\sorange\1/ matches 'apple, orange,' in "apple, orange, cherry, peach."

.   Any single character except newlines
abc A sequence of characters
(abc)   A group
a|b|c   Any one of several patterns
\d  Any digit character
\w  An alphanumeric character (“word character”)
\s  Any whitespace character
\b  A word boundary
^   Start of input
$   End of input
^$  line without chars

1. BACKREFFERENCING: Find word duplicates - /\b(\w+)\s+\1\b/
This This helper validates attributes against a block. It doesn't have a predefined validation function. You should create one using a block, and every attribute passed to validates_each will be tested against it it. In the following example, we don't want names and surnames to begin begin with lower case.

2. HTML: find target="_blank" attribute duplicate in html-php code - /<a.+?target="_blank".+?target="_blank".+?[^?]>/
<a target="_blank" style="font-family:arial,sans-serif;font-size:15px;line-height:21px;color:#5f230a;text-decoration:none;" href="<?= $highlight['NewsLetter']['url'] ?>" target="_blank">

3. Email validation
4. BASICS::CHAR_CLASSES : find all word that has foo in the middle
5. BASICS::CHAR_CLASSES : regex that matches dates like 19.06.2000
6. Word in quotes /"[^"]*"/
7. Find price in $12.33 like in text: /\$[0-9]+(\.[0-9]+)?/