JavaScript.The.Definitive.Guide—Core Javascript-basic Data Types

Table 3-1. Special numeric constants

Constant	Meaning
Infinity	Special value to represent infinity
NaN	Special not-a-number value
Number.MAX_VALUE	Largest representable number
Number.MIN_VALUE	Smallest (closest to zero) representable number
Number.NaN	Special not-a-number value
Number.POSITIVE_INFINITY	Special value to represent infinity
Number.NEGATIVE_INFINITY	Special value to represent negative infinity

Table 3-2. JavaScript escape sequences

Sequence	Character represented
\0	The NUL character (\u0000).
\b	Backspace (\u0008).
\t	Horizontal tab (\u0009).
\n	Newline (\u000A).
\v	Vertical tab (\u000B).
\f	Form feed (\u000C).
\r	Carriage return (\u000D).
\"	Double quote (\u0022).
\'	Apostrophe or single quote (\u0027).
\\	Backslash (\u005C).
\xXX	The Latin-1 character specified by the two hexadecimal digits XX.
\uXXXX	The Unicode character specified by the four hexadecimal digits XXXX.
\XXX	The Latin-1 character specified by the octal digits XXX, between 1 and 377. Not supported by ECMAScript v3; do not use this escape sequence.

Converting Numbers to Strings

一、var n_as_string = n + "";

二、var string_value = String(number);

三、string_value = number.toString( );

convert numbers in other bases

var n = 17;  

binary_string = n.toString(2); // Evaluates to "10001"

octal_string = "0" + n.toString(8); // Evaluates to "021"

hex_string = "0x" + n.toString(16); // Evaluates to "0x11"

 

Converting Strings to Numbers

var product = "21" * "2"; // product is the number 42.

var number = string_value - 0;

var number = Number(string_value);  

parseInt("3 blind mice"); // Returns 3  

parseInt("11", 2); // Returns 3 (1*2 + 1)

parseInt("zz", 36); // Returns 1295 (35*36 + 35 

parseFloat("3.14 meters"); // Returns 3.14

 

object

image.width  

image.height

image["width"]  

image["height"]

document.write("this is a test");

var point = new Object( );  

point.x = 2.3; point.y = -1.2;

var point = { x:2.3, y:-1.2 };

var rectangle = { upperLeft: { x: 2, y: 2 }, lowerRight: { x: 4, y: 4} };

var square = { "upperLeft": { x:point.x, y:point.y }, 'lowerRight': { x:(point.x + side), y:(point.y+side) }}; 

 

Array

var arr=new Array();

arr[0]="a";

arr[1]="b";  

 

 

Table 3-3. Automatic datatype conversions

Value	Context in which value is used
	String	Number	Boolean	Object
Undefined value	"undefined"	NaN	false	Error
null	"null"	0	false	Error
Nonempty string	As is	Numeric value of string or NaN	TRue	String object
Empty string	As is	0	false	String object
0	"0"	As is	false	Number object
NaN	"NaN"	As is	false	Number object
Infinity	"Infinity"	As is	true	Number object
Negative infinity	"-Infinity"	As is	TRue	Number object
Any other number	String value of number	As is	true	Number object
true	"true"	1	As is	Boolean object
false	"false"	0	As is	Boolean object
Object	toString( )	valueOf( ), toString( ), or NaN	true	As is