FB 下載回來的資訊有夠坑人，好好的 utf-8 byte 被編成 \u00??，想解讀聊天紀錄都很不方便。 https://blog.stoneapp.tech/post.php?pid=139

fb-json-decoder.js

/* required ES6 */

var fs = require('fs');
var path = require('path');
var json = JSON.parse(fs.readFileSync(path.resolve(__dirname, "./message.json"), 'utf8'));
var messages = json["messages"];
/* var messages = [
    {
      "sender_name": "Tony Yang",
      "timestamp": 1526469371,
      "content": "\u00e5\u00a6\u0082\u00e6\u009e\u009c\u00e6\u009c\u0089\u00e7\u009c\u008b\u00e5\u0088\u00b0\u00e7\u009a\u0084\u00e8\u00a9\u00b1\u00e5\u00b9\u00ab\u00e6\u0088\u0091\u00e5\u00a1\u00ab\u00e4\u00b8\u0080\u00e4\u00b8\u008b \u00e6\u0084\u009f\u00e8\u00ac\u009d",
      "type": "Generic"
    },
    {
      "sender_name": "Tony Yang",
      "timestamp": 1526469357,
      "content": "https://www.surveycake.com/s/wb7mP",
      "share": {
        "link": "https://www.surveycake.com/s/wb7mP"
      },
      "type": "Share"
    }];
*/
var result = [];

for (msg of messages) {
    result.push(decodeJson(msg));
}
json = decodeJson(json);

json["messages"] = result;
fs.writeFileSync(path.resolve(__dirname,"./output.json"), JSON.stringify(json,null,2));

function decodeJson(encoded) {
    for (item in encoded) {
        if (["sender_name","content","participants","title"].indexOf(item) == -1) {
            continue;
        }
        if (item == "participants") {
            tmp = []
            for (person of encoded[item]) {
                tmp.push(unescape(decode(String(person))));
            }
            encoded[item] = tmp;
            continue;
        }
        encoded[item] = unescape(decode(String(encoded[item])));
    }
    return encoded;
}

function decode(encodedTxt) {
    var decodedContent = "";
    var tmpArr = [];
    for (char of encodedTxt) {
        code = char.charCodeAt(0)
        if ((code > 31 && code < 127) || code == 10) {
            decodedContent+=char;
        } else {
            if (tmpArr.length == 0) {
                if (code >= 192 && code <= 223) {
                    len = 2;
                } else if (code >= 224 && code <= 239) {
                    len = 3;
                } else if (code >= 240 && code <= 247) {
                    len = 4;
                }
            }
            tmpArr.push(char);
            if (tmpArr.length == len) {
                decodedContent += utf8ToText(tmpArr,len);
                tmpArr = [];
            }
        }
    }
    return decodedContent;
}

function utf8ToText(array,len){
    var charCode = 0;
    for (index = 0; index < array.length; index++) {
        charByte = array[index].charCodeAt(0);
        switch (len) {
            case 2:
                switch (index) {
                    case 0: // first
                        charCode = charCode | ((charByte ^ 192) << 6);
                        break;
                    case 1: // sec
                        charCode = charCode | (charByte ^ 128);
                        break;
                }
                break;
            case 3:
                switch (index) {
                    case 0: // first
                        charCode = charCode | ((charByte ^ 224) << 12);
                        break;
                    case 1: // sec
                        charCode = charCode | ((charByte ^ 128) << 6);
                        break;
                    case 2: // third
                        charCode = charCode | (charByte ^ 128);
                        break;
                }
                break;
            case 4:
                switch (index) {
                    case 0: // first
                        charCode = charCode | ((charByte ^ 240) << 18);
                        break;
                    case 1: // sec
                        charCode = charCode | ((charByte ^ 128) << 12);
                        break;
                    case 2: // third
                        charCode = charCode | ((charByte ^ 128) << 6);
                        break;
                    case 3: // forth
                        charCode = charCode | (charByte ^ 128);
                        break;
                }
                break;
        }
    }
    return String.fromCodePoint(charCode);
}