6.1.1 Operator is

The is operator appears in expressions of the form:

v is T

The is operator checks to see if the value on the left is a member of the type on the right. For user-defined types and most built-in types, is returns true if the value is an instance of a class that is or derives from the type on the right, otherwise it returns false. For built-in numeric types the result cannot be determined by the class of the value. The implementation must check the actual value to see if it is included in the value set of the type.

The following table shows the results of using various values and types with the is operator:

Value	String	Number	int	uint	Boolean	Object
{}	false	false	false	false	false	true
"string"	true	false	false	false	false	true
"10"	true	false	false	false	false	true
null	false	false	false	false	false	false
undefined	false	false	false	false	false	false
true	false	false	false	false	true	true
false	false	false	false	false	true	true
0	false	true	true	true	false	true
1	false	true	true	true	false	true
-1	false	true	true	false	false	true
1.23	false	true	false	false	false	true
-1.23	false	true	false	false	false	true
NaN	false	true	false	false	false	true

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