Comprehensive JavaScript Development Technology Chapter 4 Direct Quantities and Character Sets_Basic Knowledge

4.1 String literal
1. String literal
. Can be 0 or more.
. Strings must be written on the same line. If it is too long, use the symbol
. The double quotes and single quotes used to delimit the beginning and end must match
2. Escape characters in strings

转义字符	所代表的字符
'	单引号
"	双引号
\	反斜杠
b	退格符
f	换页符
n	换行符
r	回车符
t	水平制表符
v	垂直制表符
xXX	由2位十六进制(xx)指定的latin-1字符
XXX	由1位到3位的八进制(1-377)指定的latin-1字符
UXXXX	由4位十六进制数（xxxx)指定的unicode字符

4.2 Digital direct quantity
1. Integer direct quantity var a=10;
1. Decimal integer
2 The first digit of the octal integer must be 0, 02, 0123, 047, Note: ECMAScript Not supported
3 Hexadecimal integers starting with ox or 0x, ox123, ox12AF
2. Floating point direct quantity
1. Traditional notation 12.345.2943 0.38
2. Scientific notation Method 1.23e4=1.23x103=1230
4.3 Boolean direct quantity
4.4 Array direct quantity
var myarr=["my string",,123,];
4.5 Function direct quantity
function (Parameter list)｛Statement block in function｝
var myFunction=Function(a,b){return a b};
4.6 Object direct quantity
｛Attribute name 1: attribute value 1, attribute name 2 : Attribute value 2, attribute name 3, attribute value 3....}
var myobj={height:10,width:20,name:"box"};
4.7 Special direct quantity
1.null direct quantity
var my=null;
2.undefined direct quantity
var mynumber=123;
document.writer(mynumber);
mynumber=undefined;
document .writer(mynumber);//Equivalent to the unassigned state
4.8 Character set
Javascript uses the Unicode character set
1. Unicode character set
For developers who do not belong to the English language , using the Unicode character set is a very important thing