将数组转化为字符串：join()&toString()

    var a = [ "David", "Cynthia", "Raymond", "Clayton", "Mike", "Jennifer" ];
    var a1 = a.join();
    alert(a1); // David,Cynthia,Raymond,Clayton,Mike,Jennifer
    alert(typeof a1)//string
    a2 = a.toString();
    alert(a2); // David,Cynthia,Raymond,Clayton,Mike,Jennifer
    alert(typeof a2);//string

 补充：join()方法的另一种运用：

    var a = [ "David", "Cynthia", "Raymond", "Clayton", "Mike", "Jennifer" ];
    var a1 = a.join("-****-");
    document.write(a1); // David-****-Cynthia-****-Raymond-****-Clayton-****-Mike-****-Jennifer