20916d9dc7
As the task uses multiline HTML and the note at the end suggests using `s` flag, the lazy quantifier would be safer.
36 lines
1.5 KiB
Markdown
36 lines
1.5 KiB
Markdown
In order to insert after the `<body>` tag, we must first find it. We can use the regular expression pattern `pattern:<body.*?>` for that.
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In this task we don't need to modify the `<body>` tag. We only need to add the text after it.
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Here's how we can do it:
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```js run
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let str = '...<body style="...">...';
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str = str.replace(/<body.*?>/, '$&<h1>Hello</h1>');
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alert(str); // ...<body style="..."><h1>Hello</h1>...
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```
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In the replacement string `$&` 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>`.
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An alternative is to use lookbehind:
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```js run
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let str = '...<body style="...">...';
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str = str.replace(/(?<=<body.*?>)/, `<h1>Hello</h1>`);
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alert(str); // ...<body style="..."><h1>Hello</h1>...
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```
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As you can see, there's only lookbehind part in this regexp.
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It works like this:
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- At every position in the text.
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- Check if it's preceeded by `pattern:<body.*?>`.
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- If it's so then we have the match.
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The tag `pattern:<body.*?>` won't be returned. The result of this regexp is literally an empty string, but it matches only at positions preceeded by `pattern:<body.*?>`.
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So we replaces the "empty line", preceeded by `pattern:<body.*?>`, with `<h1>Hello</h1>`. That's the insertion after `<body>`.
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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.
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