November 2021
Intermediate to advanced
784 pages
12h 13m
Japanese
Content preview from JavaScript 第7版Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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2章字句構造
プログラムの記述方法を規定する基礎的なルールの集まりを、プログラミング言語の字句構造と呼びます。例えば、変数名の表記法、コメントの区切り文字、複数のプログラム文の区切り方などを規定するものです。本章ではJavaScriptの字句構造について説明します。本章で説明するのは以下のような内容です。
- 大文字小文字の区別、空白、改行
- コメント
- リテラル
- 識別子と予約語
- Unicode
- 省略可能なセミコロン
2.1 JavaScriptプログラムのテキスト
JavaScriptは、大文字と小文字を区別します。キーワードや変数、関数名、識別子で、大文字と小文字は厳密に区別されます。例えば、whileキーワードであれば、必ず小文字で入力しなければなりません。「While」や「WHILE」は無効になります。言い換えると、online、Online、OnLine、ONLINEは、それぞれ異なる変数名として扱われます。
JavaScriptは、プログラム内のトークンを区切る空白を無視します。また、一般的には改行も無視します（ただし、例外があります。それについては§2.6を参照）。つまり、プログラム内に空白や改行を自由に挿入できます。インデントを施してプログラムを整形することで、コードを読みやすくすることができます。
通常のスペース文字（\u0020）のほかに、タブ（\u0009）やASCII制御文字、Unicodeのさまざまな空白文字も、JavaScriptでは空白として取り扱われます。また、JavaScriptは、改行文字、復帰文字、復帰文字と改行文字が連続する場合も、すべて行末記号として扱います。
2.2 コメント
JavaScriptのコメント記述方法は2通りあります。まず、JavaScriptは、 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.