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1.2. 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.


Whitespace

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


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.


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.


Identifiers

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:

i
my_variable_name
v13
$str


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

for

this

case

function

true

continue

if

typeof

default

import

var

delete

in

void

do

new

while

else

null

with

export

return


false

switch




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