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minor fixes

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This commit is contained in:
Ilya Kantor 2020-01-19 20:32:27 +01:00
parent b5ea34c83a
commit 6384ccba05
3 changed files with 25 additions and 11 deletions
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24
9-regular-expressions/14-regexp-lookahead-lookbehind/2-insert-after-head/solution.md
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@ -1,8 +1,9 @@
In order to insert after the `<body>` tag, you must first find it. We will use the regular expression pattern `pattern:<body.*>`.
In order to insert after the `<body>` tag, we must first find it. We can use the regular expression pattern `pattern:<body.*>` for that.
Next, we need to leave the `<body>` tag in place and add text after it.
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:
This can be done like this:
```js run
let str = '...<body style="...">...';
str = str.replace(/<body.*>/, '$&<h1>Hello</h1>');
@ -10,9 +11,9 @@ str = str.replace(/<body.*>/, '$&<h1>Hello</h1>');
alert(str); // ...<body style="..."><h1>Hello</h1>...
```
In the replacement string `$&` means the match itself, that is, we replace `pattern:<body.*>` Is replaced by itself plus `<h1>Hello</h1>`.
In the replacement string `$&` 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 retrospective validation:
An alternative is to use lookbehind:
```js run
let str = '...<body style="...">...';
@ -21,8 +22,15 @@ str = str.replace(/(?<=<body.*>)/, `<h1>Hello</h1>`);
alert(str); // ...<body style="..."><h1>Hello</h1>...
```
Such a regular expression at each position will check if `pattern:<body.*>`does not go directly in front of it. If yes, a match is found. But the tag `pattern:<body.*>` does not coincide, it only participates in the verification. And there are no other characters after checking in it, so the match text will be empty.
As you can see, there's only lookbehind part in this regexp.
This replaces the "empty line", followed by `pattern:<body.*>` With `<h1>Hello</h1>`. Which, exactly, is the insertion of this line after `<body>`.
It works like this:
- At every position in the text.
- Check if it's preceeded by `pattern:<body.*>`.
- If it's so then we have the match.
P.S. The flags: `pattern:/<body.*>/si`, will not interfere with this regular expression, so that a line break appears in the "dot" (a tag can span several lines), and also that the tags are in a different register of the `match:<BODY>` type, too.
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>`.
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.

6
9-regular-expressions/14-regexp-lookahead-lookbehind/2-insert-after-head/task.md
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@ -1,8 +1,8 @@
# Insert After Head
There is a line with an HTML Document.
We have a string with an HTML Document.
Insert after tag `<body>` (it may have attributes) line `<h1>Hello</h1>`.
Write a regular expression that inserts `<h1>Hello</h1>` immediately after `<body>` tag. The tag may have attributes.
For instance:
@ -20,7 +20,7 @@ let str = `
str = str.replace(regexp, `<h1>Hello</h1>`);
```
After that value `str`:
After that the value of `str` should be:
```html
<html>
<body style="height: 200px"><h1>Hello</h1>