sort object properties and JSON.stringify

Question

The simpler, modern and currently browser supported approach is simply this:

JSON.stringify(sortMyObj, Object.keys(sortMyObj).sort());

However, this method does remove any nested objects that aren't referenced and does not apply to objects within arrays. You will want to flatten the sorting object as well if you want something like this output:

{"a":{"h":4,"z":3},"b":2,"c":1}

You can do that with this:

var flattenObject = function(ob) {
    var toReturn = {};
    
    for (var i in ob) {
        if (!ob.hasOwnProperty(i)) continue;
        
        if ((typeof ob[i]) == 'object') {
            var flatObject = flattenObject(ob[i]);
            for (var x in flatObject) {
                if (!flatObject.hasOwnProperty(x)) continue;
                
                toReturn[i + '.' + x] = flatObject[x];
            }
        } else {
            toReturn[i] = ob[i];
        }
    }
    return toReturn;
};
var myFlattenedObj = flattenObject(sortMyObj);
JSON.stringify(myFlattenedObj, Object.keys(myFlattenedObj).sort());

To do it programmatically with something you can tweak yourself, you need to push the object property names into an array, then sort the array alphabetically and iterate through that array (which will be in the right order) and select each value from the object in that order. "hasOwnProperty" is checked also so you definitely have only the object's own properties. Here's an example:

var obj = {"a":1,"b":2,"c":3};

function iterateObjectAlphabetically(obj, callback) {
    var arr = [],
        i;
    
    for (i in obj) {
        if (obj.hasOwnProperty(i)) {
            arr.push(i);
        }
    }

    arr.sort();
    
    for (i = 0; i < arr.length; i++) {
        var key = obj[arr[i]];
        //console.log( obj[arr[i]] ); //here is the sorted value
        //do what you want with the object property
        if (callback) {
            // callback returns arguments for value, key and original object
            callback(obj[arr[i]], arr[i], obj);
        }
    }
}

iterateObjectAlphabetically(obj, function(val, key, obj) {
    //do something here
});

Again, this should guarantee that you iterate through in alphabetical order.

Finally, taking it further for the simplest way, this library will recursively allow you to sort any JSON you pass into it: https://www.npmjs.com/package/json-stable-stringify

var stringify = require('json-stable-stringify');
var obj = { c: 8, b: [{z:6,y:5,x:4},7], a: 3 };
console.log(stringify(obj));

Output

{"a":3,"b":[{"x":4,"y":5,"z":6},7],"c":8}

I don't understand why the complexity of the current best answers is needed, to get all the keys recursively. Unless perfect performance is needed, it seems to me that we can just call JSON.stringify() twice, the first time to get all the keys, and the second time, to really do the job. That way, all the recursion complexity is handled by stringify, and we know that it knows its stuff, and how to handle each object type :

function JSONstringifyOrder( obj, space )
{
    var allKeys = [];
    var seen = {};
    JSON.stringify(obj, function (key, value) {
        if (!(key in seen)) {
            allKeys.push(key);
            seen[key] = null;
        }
        return value;
    });
    allKeys.sort();
    return JSON.stringify(obj, allKeys, space);
}

I think that if you are in control of the JSON generation (and it sounds like you are), then for your purposes this might be a good solution: json-stable-stringify

From the project website:

deterministic JSON.stringify() with custom sorting to get deterministic hashes from stringified results

If the JSON produced is deterministic you should be able to easily diff/merge it.

You can pass a sorted array of the property names as the second argument of JSON.stringify():

JSON.stringify(obj, Object.keys(obj).sort())

Update 2018-7-24:

This version sorts nested objects and supports array as well:

function sortObjByKey(value) {
  return (typeof value === 'object') ?
    (Array.isArray(value) ?
      value.map(sortObjByKey) :
      Object.keys(value).sort().reduce(
        (o, key) => {
          const v = value[key];
          o[key] = sortObjByKey(v);
          return o;
        }, {})
    ) :
    value;
}


function orderedJsonStringify(obj) {
  return JSON.stringify(sortObjByKey(obj));
}

Test case:

  describe('orderedJsonStringify', () => {
    it('make properties in order', () => {
      const obj = {
        name: 'foo',
        arr: [
          { x: 1, y: 2 },
          { y: 4, x: 3 },
        ],
        value: { y: 2, x: 1, },
      };
      expect(orderedJsonStringify(obj))
        .to.equal('{"arr":[{"x":1,"y":2},{"x":3,"y":4}],"name":"foo","value":{"x":1,"y":2}}');
    });

    it('support array', () => {
      const obj = [
        { x: 1, y: 2 },
        { y: 4, x: 3 },
      ];
      expect(orderedJsonStringify(obj))
        .to.equal('[{"x":1,"y":2},{"x":3,"y":4}]');
    });

  });

---

Deprecated answer:

A concise version in ES2016. Credit to @codename , from https://stackoverflow.com/a/29622653/94148

function orderedJsonStringify(o) {
  return JSON.stringify(Object.keys(o).sort().reduce((r, k) => (r[k] = o[k], r), {}));
}

https://gist.github.com/davidfurlong/463a83a33b70a3b6618e97ec9679e490

const replacer = (key, value) =>
    value instanceof Object && !(value instanceof Array) ? 
        Object.keys(value)
        .sort()
        .reduce((sorted, key) => {
            sorted[key] = value[key];
            return sorted 
        }, {}) :
        value;

This is same as Satpal Singh's answer

function stringifyJSON(obj){
    keys = [];
    if(obj){
        for(var key in obj){
            keys.push(key);
        }
    }
    keys.sort();
    var tObj = {};
    var key;
    for(var index in keys){
        key = keys[index];
        tObj[ key ] = obj[ key ];
    }
    return JSON.stringify(tObj);
}

obj1 = {}; obj1.os="linux"; obj1.name="X";
stringifyJSON(obj1); //returns "{"name":"X","os":"linux"}"

obj2 = {}; obj2.name="X"; obj2.os="linux";
stringifyJSON(obj2); //returns "{"name":"X","os":"linux"}"