js拼接字符串,字符串转数组

想要把字符串按一定的规则拼起来如 1,2,3

var a = [];

a.push(1);
a.push(2);
a.push(3);

a.join(\',\');

=>> 1,2,3

想要把\'1,2,3\' 转成字符串 ["1", "2", "3"] 字符串分割

var a = \'1,2,3\';

a.split(\',\')

=>> ["1", "2", "3"]