一、5個(gè)falsy值

   0
  NaN
  ' ' 
 null
 undefined

二、類型轉(zhuǎn)換

1.轉(zhuǎn)換為字符串

number轉(zhuǎn)換為string

var n = 1
undefined
n.toString()
"1"

1+''
"1"

''+1
"1"

var n = 1
undefined
window.String(n)
"1"

boolean轉(zhuǎn)換為string

var b = true
undefined
b.toString()
"true"

true+''
"true"

''+true
"true"

window.String(true)
"true"

object轉(zhuǎn)換為string

var object = {"name":"frank"}
undefined
object.toString()
"[object Object]"

object+''
"[object Object]"

 ''+object
"[object Object]"

window.String({})
"[object Object]"

null轉(zhuǎn)換為字符串

  window.String(null)
  "null"

  ''+null
   "null"

undefined轉(zhuǎn)換為字符串

  window.String(undefined)
  "undefined"

  ''+undefined
  "undefined"

2.轉(zhuǎn)換為boolen值

  Boolean(1)
  true

  Boolean(0)
  false

  Boolean('aaa')
  true

  Boolean('')
  false

  Boolean('     ')
  true

  Boolean(null)
  false

  Boolean(undefined)
  false

  Boolean({})
  true

  Boolean({name:"frank"})
  true


  !!true
  true

  !!false
  false

  !!"123"
  true

  !!''
  false

  !!'   '
  true

  !!null
  false

  !!undefined
  false

  !!{}
  true

  !!{name:'frank'}
  true

3.轉(zhuǎn)換為Number

Number('1')
1

parseInt('1.23',10)
1

parseFloat('2.3334')
2.3334

'1'-0
1

'1.23'-0
1.23

+'1.23'
1.23

+'-3.566'
-3.566

-(-'1')
1

-(-'-1')
-1

parseInt('011')
11

parseInt('011',8)
9

parseInt('011',16)
17

parseInt('s')
NaN

parseInt('1s')
1

parseInt('12s')
12

三、四個(gè)關(guān)于內(nèi)存的題目

image.png

image.png

image.png

image.png

四、垃圾回收

image.png