string_decoder 模块提供了一个 API，用于把 Buffer 对象解码成字符串。
对于参数末尾不完整的多字节字符，string_decoder会将其保存在内部的buffer中，当再次解码时，补充到参数开头。
通过 const { StringDecoder } = require(‘string_decoder'); 的方式引用string_decoder模块。
目录：
new StringDecoder([encoding])
stringDecoder.write(buffer)
stringDecoder.end([buffer])
new StringDecoder([encoding])
说明：
创建一个新的StringDecoder实例，可传递encoding参数作为字符编码格式，默认为'utf8′
stringDecoder.write(buffer)
说明：
返回一个解码后的字符串，并确保返回的字符串不包含残缺的多字节字符，残缺的多字节字符会被保存在一个内部的 buffer 中，
用于下次调用 stringDecoder.write() 或 stringDecoder.end()。
buffer：待解码的Buffer
demo：
const decoder = new StringDecoder('utf8'); //字符的16进制小于0x80属于单字节 let outString = decoder.write(Buffer.from([0x78, 0x69, 0x61, 0x6f, 0x71, 0x69, 0x61, 0x6e, 0x67])); console.log(outString); //xiaoqiang //字符的16进制大于0x80属于双字节 outString = decoder.write(Buffer.from([0xC2, 0xA2])); console.log(outString); //￠ //单双字节混合，置于末尾 outString = decoder.write(Buffer.from([0x78, 0x69, 0x61, 0x6f, 0x71, 0x69, 0x61, 0x6e, 0x67, 0xC2])); console.log(outString); //xiaoqiang outString = decoder.write(Buffer.from([0xA2])); console.log(outString); //￠ //单双字节混合，置于中间 outString = decoder.write(Buffer.from([0x78, 0x69, 0x61, 0x6f, 0x71, 0xC2, 0x69, 0x61, 0x6e, 0x67])); console.log(outString); //xiaoq?iang outString = decoder.write(Buffer.from([0xA2])); console.log(outString); //? //单双字节混合，置于开始 outString = decoder.write(Buffer.from([0xC2, 0x78, 0x69, 0x61, 0x6f, 0x71, 0x69, 0x61, 0x6e, 0x67])); console.log(outString); //?xiaoqiang outString = decoder.write(Buffer.from([0xA2])); console.log(outString); //? //单双字节混合，置于末尾 outString = decoder.write(Buffer.from([0x78, 0x69, 0x61, 0x6f, 0x71, 0x69, 0x61, 0x6e, 0x67, 0xC2])); console.log(outString); //xiaoqiang outString = decoder.write(Buffer.from([0x78,0xA2])); console.log(outString); //?x?
stringDecoder.end([buffer])
说明：
以字符串的形式返回内部 buffer 中剩余的字节，残缺的字节会被替换成符合字符编码的字符
如果提供了 buffer 参数，则在返回剩余字节之前会再执行一次 stringDecoder.write()
demo：
const decoder = new StringDecoder('utf8'); //字符的16进制小于0x80属于单字节 let outString = decoder.write(Buffer.from([0x78, 0x69, 0x61, 0x6f, 0x71, 0x69, 0x61, 0x6e, 0x67])); console.log(outString); //xiaoqiang outString = decoder.end(); console.log(outString); // //单双字节混合，置于末尾 outString = decoder.write(Buffer.from([0x78, 0x69, 0x61, 0x6f, 0x71, 0x69, 0x61, 0x6e, 0x67, 0xC2])); console.log(outString); //xiaoqiang outString = decoder.end(Buffer.from([0xA2])); console.log(outString); //￠ //单双字节混合，置于末尾 outString = decoder.write(Buffer.from([0x78, 0x69, 0x61, 0x6f, 0x71, 0x69, 0x61, 0x6e, 0x67, 0xC2])); console.log(outString); //xiaoqiang outString = decoder.end(); console.log(outString); //?