JSON扁平化

1. 以前的作法
   https://codingdict.com/questions/8474

   JSON.unflatten = function(data) {
       "use strict";
       if (Object(data) !== data || Array.isArray(data))
           return data;
       var result = {}, cur, prop, idx, last, temp;
       for(var p in data) {
           cur = result, prop = "", last = 0;
           do {
               idx = p.indexOf(".", last);
               temp = p.substring(last, idx !== -1 ? idx : undefined);
               cur = cur[prop] || (cur[prop] = (!isNaN(parseInt(temp)) ? [] : {}));
               prop = temp;
               last = idx + 1;
           } while(idx >= 0);
           cur[prop] = data[p];
       }
       return result[""];
   }
   JSON.flatten = function(data) {
       var result = {};
       function recurse (cur, prop) {
           if (Object(cur) !== cur) {
               result[prop] = cur;
           } else if (Array.isArray(cur)) {
                for(var i=0, l=cur.length; i<l; i++)
                    recurse(cur[i], prop ? prop+"."+i : ""+i);
               if (l == 0)
                   result[prop] = [];
           } else {
               var isEmpty = true;
               for (var p in cur) {
                   isEmpty = false;
                   recurse(cur[p], prop ? prop+"."+p : p);
               }
               if (isEmpty)
                   result[prop] = {};
           }
       }
       recurse(data, "");
       return result;
   }

2. function flatten (obj) {
     var newObj = {};
     for (var key in obj) {
       if (typeof obj[key] === 'object' && obj[key] !== null) {
         var temp = flatten(obj[key])
         for (var key2 in temp) {
           newObj[key+"-"+key2] = temp[key2];
         }
       } else {
         newObj[key] = obj[key];
       }
     }
     return newObj;
   }

範例：

var test = {
  a: 1,
  b: 2,
  c: {
    c1: 3.1,
    c2: 3.2
  },
  d: 4,
  e: {
    e1: 5.1,
    e2: 5.2,
    e3: {
      e3a: 5.31,
      e3b: 5.32
    },
    e4: 5.4
  },
  f: 6
}

Logger.log("start");
Logger.log(JSON.stringify(flatten(test),null,2));
Logger.log("done");

輸出

[17-02-08 13:21:05:245 CST] start
[17-02-08 13:21:05:246 CST] {
  "a": 1,
  "b": 2,
  "c-c1": 3.1,
  "c-c2": 3.2,
  "d": 4,
  "e-e1": 5.1,
  "e-e2": 5.2,
  "e-e3-e3a": 5.31,
  "e-e3-e3b": 5.32,
  "e-e4": 5.4,
  "f": 6
}
[17-02-08 13:21:05:247 CST] done

3. 別人的解法

   /**
    * Recursively flattens a JSON object using dot notation.
    *
    * NOTE: input must be an object as described by JSON spec. Arbitrary
    * JS objects (e.g. {a: () => 42}) may result in unexpected output.
    * MOREOVER, it removes keys with empty objects/arrays as value (see
    * examples bellow).
    *
    * @example
    * // returns {a:1, 'b.0.c': 2, 'b.0.d.e': 3, 'b.1': 4}
    * flatten({a: 1, b: [{c: 2, d: {e: 3}}, 4]})
    * // returns {a:1, 'b.0.c': 2, 'b.0.d.e.0': true, 'b.0.d.e.1': false, 'b.0.d.e.2.f': 1}
    * flatten({a: 1, b: [{c: 2, d: {e: [true, false, {f: 1}]}}]})
    * // return {a: 1}
    * flatten({a: 1, b: [], c: {}})
    *
    * @param obj item to be flattened
    * @param {Array.string} [prefix=[]] chain of prefix joined with a dot and prepended to key
    * @param {Object} [current={}] result of flatten during the recursion
    *
    * @see https://docs.mongodb.com/manual/core/document/#dot-notation
    */
   function flatten (obj, prefix, current) {
     prefix = prefix || []
     current = current || {}
   
     // Remember kids, null is also an object!
     if (typeof (obj) === 'object' && obj !== null) {
       Object.keys(obj).forEach(key => {
         this.flatten(obj[key], prefix.concat(key), current)
       })
     } else {
       current[prefix.join('.')] = obj
     }
   
     return current
   }

https://stackoverflow.com/questions/19098797/fastest-way-to-flatten-un-flatten-nested-json-objects