1.5 KiB
In order to insert after the <body> tag, we must first find it. We can use the regular expression pattern pattern:<body.*?> for that.
In this task, we don't need to modify the <body> tag. We only need to add the text after it.
Here's how we can do it:
let str = '...<body style="...">...';
str = str.replace(/<body.*?>/, '$&<h1>Hello</h1>');
alert(str); // ...<body style="..."><h1>Hello</h1>...
In the replacement string $& means the match itself, that is, the part of the source text that corresponds to pattern:<body.*?>. It gets replaced by itself plus <h1>Hello</h1>.
An alternative is to use lookbehind:
let str = '...<body style="...">...';
str = str.replace(/(?<=<body.*?>)/, `<h1>Hello</h1>`);
alert(str); // ...<body style="..."><h1>Hello</h1>...
As you can see, there's only lookbehind part in this regexp.
It works like this:
- At every position in the text.
- Check if it's preceded by
pattern:<body.*?>. - If it's so, then we have the match.
The tag pattern:<body.*?> won't be returned. The result of this regexp is literally an empty string, but it matches only at positions preceded by pattern:<body.*?>.
So it replaces the "empty line", preceded by pattern:<body.*?>, with <h1>Hello</h1>. That's the insertion after <body>.
P.S. Regexp flags, such as pattern:s and pattern:i can also be useful: pattern:/<body.*?>/si. The pattern:s flag makes the dot pattern:. match a newline character, and pattern:i flag makes pattern:<body> also match match:<BODY> case-insensitively.