JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

var pattern = /ab+c/;
is read as ―a‖ followed by ―b‖ repeated one or more times, followed by ―c.‖ Keeping this pattern
in mind, you can see that it matches all the following strings:
abc
abbbbbc
The letters abc begin the alphabet
Conversely, the pattern does not match the string ―ac‖ because it does not contain at least one
―b‖ between ―a‖ and ―c.‖
The ? quantifier indicates that the previous item may occur zero times or one time, but no more.
For example:
var pattern = /ab?c/;
Read this pattern as ―a‖ followed by zero or one ―b‖s followed by ―c.‖ It matches ―ac‖ and ―abc,‖
but not ―abbc.‖ The ? essentially denotes that the preceding item is optional.
The repetition quantifiers so far haven‘t provided any way to specify that a particular character
is to be repeated some exact number of times. Curly braces ({ }) are used to indicate the
number of repetitions allowed for the preceding token (character). For example,
var pattern = /ab{5}c/;
specifies a pattern consisting of an ―a‖ followed by exactly five ―b‖ characters and then the letter
―c.‖ Of course, this particular expression could have also been written as
var pattern = /abbbbbc/;
But this ―long‖ version would be very cumbersome if you wanted to match, say, a character
repeated 25 times.
Using the curly braces it is possible to precisely indicate that the number of repetitions falls
within a specific range. To do so, list inside the curly braces the fewest number of repetitions
allowed followed by a comma and the maximum allowed. For example,
var pattern = /ab{5,7}c/;
creates a regular expression matching a single ―a‖ followed by between five and seven
(inclusive) ―b‖ characters and then the letter ―c.‖
Omitting the maximum amount from within the curly braces (but still including the comma)
specifies a minimum number of repetitions. For example,
var pattern = /ab{3,}c/;
creates an expression matching an ―a‖ followed by three or more letter ―b‖ characters followed
by a ―c.‖
The full list of repetition quantifiers is summarized in Table 8-3.
Table 8-3: Repetition Quantifiers
Character Meaning
>* Match previous item zero or more times.
>+ Match previous item one time or more.
>? Match previous item zero or one times.