JavaScript-join连接符

  1.转字符串:2种
     1.将数组中每个元素都转为字符串,再用逗号分隔:var str=String(arr);
     2.将数组中每个元素都字符串，再用自定义下标连接每个元素
      var str=arr.join("自定义连接符")
     //无缝拼接
     var chars=["H","e","l","l","o"];
     console.log(chars.join(""));
     //单词拼接为句子
     var words=["no","zuo","no","die"];
     console.log(words.join(" "));//"空格"
     //判断是否为空数组
     var arr=[,,,,,,,,];
     console.log(arr);
     //动态生成页面元素
     var provs=["北京","南京","上海"];
     var html="<option>"+provs.join("</option>")+"</option>";
     //设置id为sel的元素开始标签到结束标签之间的内容为html
     sel.innerHTML="<option>请选择</option>"