Microsoft® JScript™  Operator 
Language Reference Version 1

Used to find the difference between two numbers or to indicate the negative value of a numeric expression.
result = number1  number2
numberThe  operator syntax has these parts:
Part Description result Any numeric variable. number Any numeric expression. number1 Any numeric expression. number2 Any numeric expression.
In Syntax 1, the  operator is the arithmetic subtraction operator used to find the difference between two numbers. In Syntax 2, the  operator is used as the unary negation operator to indicate the negative value of an expression.For information on when a runtime error is generated by Syntax 1, see the Operator Behavior table.
For Syntax 2, as for all unary operators, expressions are evaluated as follows:
The operator is applied to the resulting number. In Syntax 2, if the resulting number is nonzero, result is equal to the resulting number with its sign reversed. If the resulting number is zero, result is zero.
 If applied to undefined or null expressions, a runtime error is raised.
 Objects are converted to strings.
 Strings are converted to numbers if possible. If not, a runtime error is raised.
 Boolean values are treated as numbers (0 if false, 1 if true).