javascript

Chapter 22: The Evolution of JavaScript
Strings may be declared as being the type string or String . The only difference between these two is
that variables declared as string cannot be set to null , whereas variables declared as String can. Here
is an example:
var name : string = “Nicholas”;
var anotherName : string = null;
//error!
var title : String = “Professional JavaScript”;
var publisher : String = null; //OK
In this example, the variables name and anotherName cannot be set to null ; if you attempt to make
them so, an error occurs. If a variable declared as String is not initialized, then it is given the value of
null , which is different from ECMAScript 3 where uninitialized variables always hold the value
undefined .
The same holds true for Boolean values that may be declared as either boolean or Boolean . When a
variable is declared as boolean , it cannot be set to null , whereas Boolean variables can be set to null .
Generally, types that begin with a lowercase letter aren ’ t nullable, whereas those beginning with an
uppercase letter are.
The biggest difference between types in ECMAScript 3 and 4 comes with numbers. In ECMAScript 3, all
numbers are represented by the Number type. ECMAScript 4 introduces the following, more specific
number types:
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int — Whole numbers in the range - 2147483648 through 2147483647.
uint — Whole numbers in the range 0 through 4294967295.
double — 64 - bit IEEE binary floating - point values; effectively the same as primitive numbers in
ECMAScript 3.
decimal — 128 - bit IEEE binary floating - point values. Arithmetic with these values is more
precise than with double .
None of these data types are nullable, though there is a Number type that can be used when null is a
valid option. The Number type is the equivalent of Number in ECMAScript 3 and contains a nullable
64 - bit IEEE binary floating - point value. Here are some examples:
var length : Number = 5;
var size : Number = null;
var area : Number = 125.9;
var age : uint = 29;
var distance : double = 54.3;
var average : decimal = 1.23;
var temperature : int = -32;
Numeric literals are interpreted to be specific data types. Any hexadecimal literal (beginning with 0x) is
considered to be a uint , whereas most whole numbers are considered int . If a positive number is in the
range for uint but not in the range of int , the number becomes a uint . All other values are considered
to be doubles for backwards compatibility with ECMAScript 3. You can force the interpreter to treat a
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