Javascript类型转换

参考：http://www.jb51.net/article/32601.htm

经过实际代码验证结果如下。

三大类型转换：Boolean, Number, String

布尔量转换：

Boolean("")        =false

Boolean("s")       =true

Boolean(0)           =false

Boolean(1)           =true

Boolean(-1)          =true

Boolean(null)        =false

Boolean(undefined)   =false

Boolean(new Object())=true数值转换：

Number(false)        =0

Number(true)         =1

Number(undefined)    =NaN

Number(null)         =0

Number("1.2")        =1.2

Number("12")         =12

Number("1.2.3")      =NaN

Number(new Object()) =NaN字符串转换：var s1 = nullvar s2 = String(t1);//nullvar s3 = s1.toString();//报错var s4var s5 = String(t4);//报错：t4未定义var s6 = t4.toString();//报错：t4未定义