The following are the rules for naming JavaScript variables:

1.
A variable name cannot start with a numeral. For instance, 3x or
2goats or
76trombones would all be
illegal variable names.

You can, however, have numbers within a JavaScript variable name; for instance
up2me or
go4it would both be perfectly valid variable names.

不能以数字开头

2.
You cannot have a mathematical or logical operator in a variable name. For instance,
2*something or
this+that would both be illegal... because the * and the + are arithmetic operators. The same holds true for ^, /, \, !, etc.

变量名中不能含有操作符

3.
You must not use any punctuation marks of any kind in a JavaScript variable name, other than the
underscore; for example... some:thing or
big# or
do'to would all be
illegal.

The underscore is the exception, and it can be used at the beginning, within, or at the end of JavaScript variable names. You can use names like
_pounds or
some_thing or
gallons_ as variable names and they are perfectly legal.

变量名中不能有标点符号，除了_下划线以外的任何标点符号。

4.
JavaScript names must not contain spaces. Ever.

变量名中不能有空格

5.
You cannot use JavaScript keywords (parts of the language, itself) for variable names. Thus
window or
open or
location
or string
would be illegal.  Check a JavaScript reference if in
doubt as to whether something is or is not part of the language --
JavaScript has grown into a fairly fully-fleshed language, so you
may get some occasional surprises.

You can, of course, use what are otherwise keywords as parts of variable names. For instance,
thatWindow or
someString or
theLocation would all be perfectly acceptable.

变量中不能用JavaScript语言的关键词。如 window，string,blooean等等

6.
JavaScript variable names are case-sensitive. Programmers in other languages are often tripped up by this one, as some languages are not sensitive to case in variable names.

For instance, all of the following names would be considered completely different variable names in JavaScript: 
gasbag 
Gasbag  GasBag  gasBag

变量名区分大小写.