js string转uint8array

手写转换：

function toUint8Arr(str) {
            const buffer = [];
            for (let i of str) {
                const _code = i.charCodeAt(0);
                if (_code < 0x80) {
                    buffer.push(_code);
                } else if (_code < 0x800) {
                    buffer.push(0xc0 + (_code >> 6));
                    buffer.push(0x80 + (_code & 0x3f));
                } else if (_code < 0x10000) {
                    buffer.push(0xe0 + (_code >> 12));
                    buffer.push(0x80 + (_code >> 6 & 0x3f));
                    buffer.push(0x80 + (_code & 0x3f));
                }
            }
            return Uint8Array.from(buffer);
}

Unicode转utf8的规则：

Unicode符号范围 | UTF-8编码方式

(十六进制) | （二进制）

--------------------+---------------------------------------------

0000 0000-0000 007F | 0xxxxxxx 

0000 0080-0000 07FF | 110xxxxx 10xxxxxx

0000 0800-0000 FFFF | 1110xxxx 10xxxxxx 10xxxxxx

0001 0000-0010 FFFF | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx