如果多个均为false 则内层触发先于外层
var arr = ["a","b""2","3","str"]; var result = ("b" in arr); var result1 = (4 in arr); document.write(result); document.write(result1); 程序运行结果是?
Afalse，true
Btrue,false
Cfalse，false
Dtrue, true