按字节截取字符串

substr.js

baidu.string.getByteLength = function(source) {
    return String(source).replace(/[^\x00-\xff]/g, "ci").length;
};
/*
 * Tangram
 * Copyright 2009 Baidu Inc. All rights reserved.
 *
 * path: baidu/string/subByte.js
 * author: dron, erik
 * version: 1.1.0
 * date: 2009/11/30
 */
/**
 * 对目标字符串按gbk编码截取字节长度
 *
 * @param {string} source 目标字符串
 * @param {number} length 需要截取的字节长度
 * @return {string} 字符串截取结果
 */
baidu.string.subByte = function(source, length) {
    source = String(source);
    var getLen = baidu.string.getByteLength,
        i, len, current, next, currentLen, nextLen;
    if (length < 0 || getLen(source) <= length) {
        return source;
    }
    len = source.length;
    for (i = Math.floor(length / 2) - 1; i < len; i++) {
        current = next || source.substr(0, i);
        currentLen = nextLen || getLen(current);
        if (currentLen == length) {
            return current;
        } else {
            next = source.substr(0, i + 1);
            nextLen = getLen(next);
            if (nextLen > length) {
                return current;
            }
        }
    }
    return source;
};
这种方式的实现原理是先将中文替换成中文加个空格，这样变相的将一个中文变成了2个字节，然后在这个基础上截取，截取完成后在将中文加空格变成中文。
baidu.string.subByte1 = function(source, length) {
    return (source + '').substr(0, length).replace(/([^\x00-\xff])/g, '$1 ').substr(0, length).replace(/([^\x00-\xff]) /g, '$1');
}