1.普通写法：
不追求效率的话，其实这样写更加安全
var str = "aabbcccccddefggg";
var str_tmp = ''
var simbol_same = ''
for (var i = 0; i < str.length; i++){
if (str[i] == simbol_same) {
continue;
}
simbol_same = str[i];
str_tmp += simbol_same;
}
alert(str_tmp)
2.正则写法
var str = "aabbcccccddefggg";
str = str.replace(/(.)\1+/g, function (sameletter) { return sameletter[0] });
alert(str)
