Java Reference
In-Depth Information
You then join the string together again using the
Array
object's
join()
methods, which you saw in
Chapter 4:
document.write(myFruitArray.join("<br />"))
the replace() method
You've already looked at the syntax and usage of the
replace()
method. However, something
unique to the
replace()
method is its ability to replace text based on the groups matched in
the regular expression. You do this using the
$
sign and the group's number. Each group in a
regular expression is given a number from
1
to
99
; any groups greater than
99
are not accessible.
To refer to a group, you write
$
followed by the group's position. For example, if you had the
following:
var myRegExp = /(\d)(\W)/g;
then
$1
refers to the group
(\d)
, and
$2
refers to the group
(\W)
. You've also set the global flag
g
to
ensure that all matching patterns are replaced—not just the first one.
You can see this more clearly in the next example. Say you have the following string:
var myString = "2012, 2013, 2014";
If you wanted to change this to
"the year 2012, the year 2013, the year 2014"
, how could
you do it with regular expressions?
First, you need to work out the pattern as a regular expression, in this case four digits:
var myRegExp = /\d{4}/g;
But given that the year is different every time, how can you substitute the year value into the
replaced string?
Well, you change your regular expression so that it's inside a group, as follows:
var myRegExp = /(\d{4})/g;
Now you can use the group, which has group number
1
, inside the replacement string like this:
myString = myString.replace(myRegExp, "the year $1");
The variable
myString
now contains the required string
"the year 2012, the year 2013, the year 2014"
.
Let's look at another example in which you want to convert single quotes in text to double quotes.
Your test string is this:
He then said 'My Name is O'Connerly, yes that's right, O'Connerly'.
