avalon 过滤器 字符串截取

/**
* 对长字符串截短，以字符长度截取，中文占两字符;{{str|truncatex(4,'...')}}
* @param str
* @param length,新字符串长度（按照英文字符算，一个中文占两字符），包含truncation的字符个数
* @param truncation,新字符串的结尾的字段
* @returns {返回新字符串}
*/
avalon.filters.truncatex = function (str, length, truncation) {
    var chinese_pattern = /[u4E00-u9FA5]|[uFE30-uFFA0]/gi;
    // [u4E00-u9FA5]表示汉字，[uFE30-uFFA0]表示全角
    str = str || " ";
    length = length || 30;
    truncation = typeof truncation === "string" ? truncation : "...";
    var chineseIn = function (s) {
        return chinese_pattern.exec(s) ? true : false;
    };
    var calcSize = function (source) {
        var strTemp = source.replace(chinese_pattern, "aa");
        return strTemp.length;
    };
    var recursion = function (source, length) {
        if (calcSize(source) <= length || (!chineseIn(source))) {
            return source;
        } else {
            return recursion(source.slice(0, source.length - 1), length);
        }
    };
    var sliceLength = length - truncation.length;
    return calcSize(str) > length ? recursion(str.slice(0, sliceLength), sliceLength) + truncation : String(str);
};