一, 数据类型
1)六种数据类型
number string boolean undefined object function
1,类型转换
Number(mix)
parseInt(sting,radix)
parseFloat(string)
toString(radix):undefined 和null不能用
String(mix):写什么都变成字符串形式
Boolean()
(1) var num = [ ];
console.log(typeof(num));//object
(2) typeof(null) --->object
typeof(Object)---->object
typeof(undefined)--->undefined
(3) typeof(undefined) --->undefined
(4) var demo = true
var num = Number(demo);
console.log(typeof(num) + num);//number1
(5)var demo = "a";
var num = Number(demo);
undefined不能转换为数字类型—>NaN
a–>NaN
“-123” -->NaN
“123abc”–>NaN
null —>0
parseInt(demo);
var demo = true;
var num = parseInt(demo);
console.log(typeof(num)+":"+num);//number:NaN
null—> NaN
字符串 “123.9”–>123
var demo = "123.abc";
var num = parseInt(demo,16);
console.log(typeof(num)+":"+num);//以16进制为基底转化为10进制
看到非整数字为123截止
parseFloat 看到3以外的非数字位截止
toString(radix):undefined 和null不能用
var demo = 234;
var num = demo.toString(8);
console.log(typeof(num)+":"+num);//string:352:把123转化为8进制
隐式类型转换
isNaN() :先转化Number(‘abc’)再isNaN(NaN) :值为true false
++/-- +/-(亿元正负) :调用的是Number
- 若调动string :只要有一侧式string 就是string类型
*/% :Number 调用
&& || !
< > <= >= : 字符串和数字比较 字符串位转换为数字类型"123">"12"true
== !=
undefined和null都不> < = 0
undefined ==null true
NaN == NaN false
console.log(type(a))//字符串形式的"undefined"