// close the opening <a> tag
+
'>'
// add the contents
+
parts
[
2
]
// and the closing tag
+
'</a>'
;
}
This function is longer than it needs to be, but we’ve broken it down for clarity. Note
that even in this function, we’re using multiple regexes: one to match the parts of the
<a>
tag, one to do the split (using a regex to identify one or more whitespace charac‐
ters), and one to filter only the attributes we want. It would be much more difficult to
do all of this with a single regex.
Now for the interesting part: using
sanitizeATag
on a block of HTML that might
contain many
<a>
tags, among other HTML. It’s easy enough to write a regex to
match just the
<a>
tags:
html
.
match
(
/<a .*?>(.*?)<\/a>/ig
);
But what do we do with it? As it happens, you can pass a function to
String.proto
type.replace
as the replacement parameter. So far, we’ve only be using strings as the
replacement parameter. Using a function allows you to take special action for each
replacement. Before we finish our example, let’s use
console.log
to see how it works:
html
.
replace
(
/<a .*?>(.*?)<\/a>/ig
,
function
(
m
,
g1
,
offset
) {
console.log(
`<a> tag found at
${
offset
}
. contents:
${
g1
}
`
);
});
The function you pass to
String.prototype.replace
receives the following argu‐
ments in order:
• The entire matched string (equivalent to
$&
).
• The matched groups (if any). There will be as many of these arguments as there
are groups.
• The offset of the match within the original string (a number).
• The original string (rarely used).
The return value of the function is what gets replaced in the returned string. In the
example we just considered, we weren’t returning anything, so
undefined
will be
returned, converted into a string, and used as a replacement. The point of that exam‐
ple was the mechanics, not the actual replacement, so we simply discard the resultant
string.
Now back to our example…. We already have our function to sanitize an individual
<a>
tag, and a way to find
<a>
tags in a block of HTML, so we can simply put them
together:
252 | Chapter 17: Regular Expressions
