Mastering JavaScript

Data Structures and Manipulation
In the following example, we create a pattern where the character u is optional (has 0
or 1 occurrence):
var str = /behaviou?r/;
console.log(str.test("behaviour"));
// true
console.log(str.test("behavior"));
// true
It helps to read the /behaviou?r/ expression as 0 or 1 occurrences of character u.
The repetition quantifier succeeds the character that we want to repeat. Let's try out
some more examples:
console.log(/'\d+'/.test("'123'")); // true
You should read and interpret the \d+ expression as ' is a literal character match, \d
matches characters [0-9], the + quantifier will allow one or more occurrences, and '
is a literal character match.
You can also group character expressions using (). Observe the following example:
var heartyLaugh = /Ha+(Ha+)+/i;
console.log(heartyLaugh.test("HaHaHaHaHaHaHaaaaaaaaaaa"));
//true
Let's break the preceding expression into smaller chunks to understand what is
going on in here:
• H: literal character match
• a+: 1 or more occurrences of character a
• (: start of the expression group
• H: literal character match
• a+: 1 or more occurrences of character a
• ): end of expression group
• +: 1 or more occurrences of expression group (Ha+)
Now it is easier to see how the grouping is done. If we have to interpret the
expression, it is sometimes helpful to read out the expression, as shown in the
preceding example.
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