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Chapter 11. JavaScript > JavaScript Syntax

11.3. JavaScript Syntax

JavaScript syntax is modeled on Java syntax; Java syntax, in turn, is modeled on C and C++ syntax. Therefore, C, C++, and Java programmers should find that JavaScript syntax is comfortably familiar.

Case sensitivity

JavaScript is a case-sensitive language. All keywords are in lowercase. All variables, function names, and other identifiers must be typed with a consistent capitalization.


JavaScript ignores whitespace between tokens. You may use spaces, tabs, and newlines to format and indent your code in a readable fashion.


JavaScript statements are terminated by semicolons. When a statement is followed by a newline, however, the terminating semicolon may be omitted. Note that this places a restriction on where you may legally break lines in your JavaScript programs: you may not break a statement across two lines if the first line can be a complete legal statement on its own.


JavaScript supports both C and C++ comments. Any amount of text, on one or more lines, between /* and */ is a comment and is ignored by JavaScript. Also, any text between // and the end of the current line is a comment and is ignored. Examples:

// This is a single-line, C++-style comment.
* This is a multiline, C-style comment.
* Here is the second line.
/* Another comment. */ 
// This too.


Variable, function, and label names are JavaScript identifiers. Identifiers are composed of any number of ASCII letters and digits, and the underscore ( _ ) and dollar sign ($) characters. The first character of an identifier must not be a digit, however, and the $ character is not allowed in identifiers in JavaScript 1.0. The following are legal identifiers:



The following keywords are part of the JavaScript language and have special meaning to the JavaScript interpreter. Therefore, they may not be used as identifiers:



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