May 2020
Intermediate to advanced
706 pages
21h 15m
English
Content preview from JavaScript: The Definitive Guide, 7th Edition
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Chapter 2. Lexical Structure
The lexical structure of a programming language is the set of elementary rules that specifies how you write programs in that language. It is the lowest-level syntax of a language: it specifies what variable names look like, the delimiter characters for comments, and how one program statement is separated from the next, for example. This short chapter documents the lexical structure of JavaScript. It covers:
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Case sensitivity, spaces, and line breaks
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Comments
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Literals
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Identifiers and reserved words
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Unicode
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Optional semicolons
2.1 The Text of a JavaScript Program
JavaScript is a case-sensitive language. This means that language
keywords, variables, function names, and other identifiers must
always be typed with a consistent capitalization of letters. The
while keyword, for example, must be typed “while,” not “While”
or “WHILE.” Similarly, online, Online, OnLine, and ONLINE
are four distinct variable names.
JavaScript ignores spaces that appear between tokens in programs. For the most part, JavaScript also ignores line breaks (but see §2.6 for an exception). Because you can use spaces and newlines freely in your programs, you can format and indent your programs in a neat and consistent way that makes the code easy to read and understand.
In addition to the regular space character (\u0020), JavaScript also
recognizes tabs, assorted ASCII control characters, and various Unicode
space characters as whitespace. JavaScript recognizes newlines, ...
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