1.1 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.

1.1.1 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.

1.1.2 Whitespace

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

1.1.3 Semicolons

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.

1.1.4 Comments

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 multi-line, C-style comment.
 * Here is the second line.
 */
/* Another comment. */ // This too.

1.1.5 Identifiers

Variable, function, and label names are JavaScript identifiers. Identifiers are composed of any number of letters and digits, and _ and $ characters. The first character of an identifier must not be a digit, however. The following are legal identifiers:

i
my_variable_name
v13
$str

1.1.6 Keywords

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:

break     do        if         switch  typeof        
case      else      in         this    var   
catch     false     instanceof throw   void  
continue  finally   new        true    while 
default   for       null       try     with
delete    function  return

JavaScript also reserves the following words for possible future extensions. You may not use any of these words as identifiers either:

abstract  enum        int        short
boolean   export      interface  static
byte      extends     long       super
char      final       native     synchronized
class     float       package    throws
const     goto        private    transient
debugger  implements  protected  volatile
double    import      public

In addition, you should avoid creating variables that have the same name as global properties and methods: see the Global, Object, and Window reference pages. Within functions, do not use the identifier arguments as an argument name or local variable name.