Searching with Regular Expressions
Once we have a regex, we have multiple options for using it to search in a string.
To understand the options for replacement, we’re going to get a little preview of the
regex metalanguage—using a static string here would be very boring. We’ll use the
regex
/\w{3,}/ig
, which will match all words three letters or longer (case insensi‐
tive). Don’t worry about understanding this right now; that will come later in this
chapter. Now we can consider the search methods available to us:
const
input
=
"As I was going to Saint Ives"
;
const
re
=
/\w{3,}/ig
;
// starting with the string (input)
input
.
match
(
re
);
// ["was", "going", "Saint", "Ives"]
input
.
search
(
re
);
// 5 (the first three-letter word starts at index 5)
// starting with the regex (re)
re
.
test
(
input
);
// true (input contains at least one three-letter word)
re
.
exec
(
input
);
// ["was"] (first match)
re
.
exec
(
input
);
// ["going"] (exec "remembers" where it is)
re
.
exec
(
input
);
// ["Saint"]
re
.
exec
(
input
);
// ["Ives"]
re
.
exec
(
input
);
// null -- no more matches
// note that any of these methods can be used directly with a regex literal
input
.
match
(
/\w{3,}/ig
);
input
.
search
(
/\w{3,}/ig
);
/\w{3,}/ig
.
test
(
input
);
/\w{3,}/ig
.
exec
(
input
);
// ...
Of these methods,
RegExp.prototype.exec
provides the most information, but you’ll
find that it’s the one you use the least often in practice. I find myself using
String.prototype.match
and
RegExp.prototype.test
the most often.
Replacing with Regular Expressions
The same
String.prototype.replace
method we saw before for simple string
replacement also accepts a regex, but it can do a lot more. We’ll start with a simple
example—replacing all four-letter words:
const
input
=
"As I was going to Saint Ives"
;
const
output
=
input
.
replace
(
/\w{4,}/ig
,
'****'
);
// "As I was ****
// to **** ****"
We’ll learn about much more sophisticated replacement methods later in this chapter.
Searching with Regular Expressions | 239
