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Copy file name to clipboardExpand all lines: 1-js/05-data-types/07-map-set/article.md
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@@ -41,6 +41,12 @@ alert( map.size ); // 3
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As we can see, unlike objects, keys are not converted to strings. Any type of key is possible.
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```smart header="`map[key]` isn't the right way to use a `Map`"
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Although `map[key]` also works, e.g. we can set `map[key] = 2`, this is treating `map` as a plain JavaScript object, so it implies all corresponding limitations (no object keys and so on).
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So we should use `map` methods: `set`, `get` and so on.
In the replacement string `$&` means the match itself, that is, we replace `pattern:<body.*>` Is replaced by itself plus `<h1>Hello</h1>`.
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In the replacement string `$&` 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 retrospective validation:
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.
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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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This replaces the "empty line", followed by `pattern:<body.*>` With`<h1>Hello</h1>`. Which, exactly, is the insertion of this line after `<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. 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.
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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.
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