PHP全栈学习笔记33

undefined,null,number,Boolean,String,Object

null 本身就是一个对象
var data = null
undefined
type of data
"object"

undefined == null
true

var message = ' '
undefined

message == false
true

var message = 'jscsshtml'
undefined

message
'jscsshtml'

message.length
9

var num = 12
undefined

var numString = num.toString()
undefined

numString
"12"

typeof numString
"string"

var obj = new Object()
undefined

typeof obj
"object"

obj.url = 'dashu'
'dashu'

obj.url
'dashu'

obj.sayhello = function() {console.log('dashu')}
function() {console.log('dashu')}

obj.sayhello()
dashu

Number(' ');
0

Number('123')
123

Number(true)
1

Number('da')
NaN

function 函数名（参数列表）{
 函数体由一条或多条语句组成；
}