Skip to content

Make solution in 9.14 safer #2376

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Dec 13, 2020
Merged

Make solution in 9.14 safer #2376

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
16 changes: 8 additions & 8 deletions ...ular-expressions/14-regexp-lookahead-lookbehind/2-insert-after-head/solution.md
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,23 +1,23 @@
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 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:

```js run
let str = '...<body style="...">...';
str = str.replace(/<body.*>/, '$&<h1>Hello</h1>');
str = str.replace(/<body.*?>/, '$&<h1>Hello</h1>');

alert(str); // ...<body style="..."><h1>Hello</h1>...
```

In the replacement string `$&` means the match itself, that is, the part of the source text that corresponds to `pattern:<body.*>`. It gets replaced by itself plus `<h1>Hello</h1>`.
In the replacement string `$&` 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:

```js run
let str = '...<body style="...">...';
str = str.replace(/(?<=<body.*>)/, `<h1>Hello</h1>`);
str = str.replace(/(?<=<body.*?>)/, `<h1>Hello</h1>`);

alert(str); // ...<body style="..."><h1>Hello</h1>...
```
Expand All @@ -26,11 +26,11 @@ 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 preceeded by `pattern:<body.*>`.
- Check if it's preceeded 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 preceeded by `pattern:<body.*>`.
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.*?>`.

So we replaces the "empty line", preceeded by `pattern:<body.*>`, with `<h1>Hello</h1>`. That's the insertion after `<body>`.
So we replaces the "empty line", preceeded 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 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.
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.