Mastering JavaScript

Data Structures and Manipulation
The exec() method is useful in getting information about the match found because
it returns an object with information about the match. The object returned from
exec() has an index property that tells us where the successful match begins in the
string. This is useful in many ways:
var match = /\d+/.exec("There are 100 ways to do this");
console.log(match);
// ["100"]
console.log(match.index);
// 10
Alternatives – OR
Alternatives can be expressed using the | (pipe) character. For example, /a|b/
matches either the a or b character, and /(ab)+|(cd)+/ matches one or more
occurrences of either ab or cd.
Beginning and end
Frequently, we may wish to ensure that a pattern matches at the beginning of a
string or perhaps at the end of a string. The caret character, when used as the first
character of the RegEx, anchors the match at the beginning of the string such that
/^test/ matches only if the test substring appears at the beginning of the string
being matched. Similarly, the dollar sign ($) signifies that the pattern must appear at
the end of the string: /test$/.
Using both ^ and $ indicates that the specified pattern must encompass the entire
candidate string: /^test$/.
Backreferences
After an expression is evaluated, each group is stored for later use. These values are
known as backreferences. Backreferences are created and numbered by the order in
which opening parenthesis characters are encountered going from left to right. You
can think of backreferences as the portions of a string that are successfully matched
against terms in the regular expression.
The notation for a backreference is a backslash followed by the number of the
capture to be referenced, beginning with 1, such as \1, \2, and so on.
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