字符编码(转载)

转载: https://blog.csdn.net/guxiaonuan/article/details/78678043

// 附: 十进制数值转 utf-8 编码方法, 如果要从 Unicode 编码转 utf-8, 可通过 parseInt(unicode, 16) 得到 unicode 编码的十进制表示再转

function decimal2Utf8(num) {

    if (num < 0 || num > Math.pow(2, 31) - 1) {
        throw new Error('RangeError: param num is expect 0 ~ 2^31-1, but received ' + num)
    }

    var strs = [],
        start = 0,
        end, digit, binaryStr, biteLen, biteLen2, strLen, cur

    digit = Math.log2(num);
    binaryStr = num.toString(2);
    strLen = binaryStr.length

    if (digit < 7) {
        strs.push(binaryStr.padStart(8, '0')); 
    } else {
        biteLen = (digit - 3) % 4 === 0 ? (digit - 3) / 4 + 1 : Math.ceil((digit - 3) / 4);
        biteLen2 = biteLen;

        while(biteLen) {
            end = strLen - (biteLen - 1) * 6;
            // 如果是最高位
            if (biteLen === biteLen2) {
                cur = ''.padStart(biteLen, 1) + binaryStr.substring(start, end).padStart(8 - biteLen, '0')
            } else {
                cur = '1' + binaryStr.substring(start, end).padStart(7, '0')
            }
            strs.push(cur)

            start = end;
            biteLen--;
        }
    }

    for (var i = 0; i < strs.length; i++) {
        strs[i] = '%' + parseInt(strs[i], 2).toString(16).toUpperCase()
    }

    return strs.join('')
}

附:  

　　https://unicode-table.com/cn/blocks/

　　http://www.ruanyifeng.com/blog/2007/10/ascii_unicode_and_utf-8.html

　　https://baike.baidu.com/item/Unicode/750500?fr=aladdin