一.string是有效数字字符的字符串("123")

1.sting类型的自增,自减运算string++ => number

2.string+string/number=string

3.string-string/number = number

4.string*string/number = number

5.string+true=string

6.string-true=number;

二.string不是有效数字字符的字符串("jjj")

string-string/number =NAN