function  chang(str ,len)

         {

             function lenStat(str) {

               function isChinese(str) { //判断是不是中文

                var reCh = /[u00-uff]/;

                return !reCh.test(str);

            }

                var strlen = 0; //初始定义长度为0

                var text = str.trim();

                for(var i = 0; i < text.length; i++) {

                    if(isChinese(text.charAt(i)) == true) {

                        strlen = strlen + 2; //中文为2个字符

                    } else {

                        strlen = strlen + 1; //英文一个字符

                    }

                }

                return strlen;

            }

            var strlen = lenStat(str);

            console.log(strlen);

            var strs = '';

            for(var i = 0; i <strlen; i = i +len) {

                strs += str.substring(i, i + len) + "<br>";

            }

            return strs;

         }

            chang(str,20);

             console.log(chang(str,20));

            var sd = document.getElementById('sd');

            sd.innerHTML =chang(str,20);