abstract：var a=5;undefineda5typeof a"number"var b='8'undefinedb"8"typeof b"string"var c='dack'undefinedc"dack"typeof c"string"
var a=5;
undefined
a
5
typeof a
"number"
var b='8'
undefined
b
"8"
typeof b
"string"
var c='dack'
undefined
c
"dack"
typeof c
"string"
Correcting teacher：韦小宝Correction time：2018-12-20 10:30:25
Teacher's summary：测试的没毛病！最好还是在编辑器里测试再运行哦！