Develop Reference

How to check if an object has other than specific properties

I have an object obj which has n number of possible properties
lets say some of them are known,
const someKnownProps = ["props.abc", "xyz"]; // or more
I want to know if obj has other than known properties in it.
To clarify:
obj can look like this:
obj = {
props: {
abc: {
def: 1
},
ghi: {
jkl: 2
}
},
xyz: 3
}
Doing Object.keys only return first level children,
in this case it will return props not props.abc

You can use Object.keys to get all keys and filter the keys which aren't included in the someKnownProps array.
const obj = {
"props.abc": 1,
"xyz": 2,
"three": 3,
"four": 4,
}
const someKnownProps = ["props.abc", "xyz"]; // or more
const unknownKeys = Object.keys(obj).filter(key => !someKnownProps.includes(key))
console.log(unknownKeys)

There are two (unrelated) tasks involved in this question:
Traversal of an object's properties
Comparison of a set of traversed object properties to a list of strings representing dot-notation-formatted object property accessors
While I'm sure the former has been previously discussed on SO, I'll provide an implementation of such an algorithm below in order to address the details of this question.
This is essentially a specific case of recursion where each cycle starts with these inputs:
an object
a dot-notation-formatted path
a Set of existing such paths
The code below includes inline comments explaining what's happening, and there are some console.log statements at the end to help you visualize some example results based on the data in your question. If something is unclear after reviewing the code, feel free to leave a comment.
'use strict';
/** #returns whether value is a non-null, non-array object */
function isObject (value) {
return value !== null && typeof value === 'object' && !Array.isArray(value);
}
/** #returns the enumerable (optionally including inherited) keys of an object */
function getKeys (obj, includeInherited = false) {
if (!includeInherited) return Object.keys(obj);
const keys = new Set();
let o = obj;
while (o !== null) {
for (const key of Object.keys(o)) keys.add(key);
o = Object.getPrototypeOf(o);
}
return [...keys];
}
/**
* #returns an array of strings representing all traversible branches
* of child objects, each formatted as a combined path of dot-notation
* property accessors
*/
function findObjectPaths (
obj,
{
includeInherited = false,
currentPath = '',
paths = new Set(),
skipReturn = false,
} = {},
) {
for (const key of getKeys(obj, includeInherited)) {
// Append the current dot-notation property accessor
// to the existing path of this object:
const path = `${currentPath}.${key}`;
// Add it to the set:
paths.add(path);
const o = obj[key];
// Recurse if the child value is an object:
if (isObject(o)) {
findObjectPaths(o, {
includeInherited,
currentPath: path,
paths,
skipReturn: true,
});
}
}
// If this is not a sub-cycle (it's the top-level invocation), then convert
// the set to an array and remove the first "." from each string
if (!skipReturn) return [...paths].map(p => p.slice(1));
}
// Use:
const obj = {
props: {
abc: {
def: 1,
},
ghi: {
jkl: 2,
},
},
xyz: 3,
};
let someKnownProps = ['props.abc', 'xyz'];
let objectPaths = findObjectPaths(obj);
let hasOtherProps = objectPaths.some(path => !someKnownProps.includes(path));
console.log(hasOtherProps); // true
// An example of all of the paths in the object above:
someKnownProps = [
'props',
'props.abc',
'props.abc.def',
'props.ghi',
'props.ghi.jkl',
'xyz',
];
objectPaths = findObjectPaths(obj);
hasOtherProps = objectPaths.some(path => !someKnownProps.includes(path));
console.log(hasOtherProps); // false
// Finally, comparing the results of inherited vs non-inherited enumeration:
const objWithoutOwnProps = Object.create({
props: {
abc: {
def: 1,
},
ghi: {
jkl: 2,
},
},
xyz: 3,
});
console.log(
'Non-inherited props:',
findObjectPaths(objWithoutOwnProps),
);
console.log(
'Inherited props:',
findObjectPaths(objWithoutOwnProps, {includeInherited: true}),
);

Similar to what Mina said:
let obj = {one: 1, two: 2, three: 3};
let knownKeys = ['one', 'two'];
for (let key in obj) {
if (!knownKeys.includes(key)) {
console.log(key);
}
}

How to do a deep comparison between 2 objects with lodash?

I have 2 nested objects which are different and I need to know if they have a difference in one of their nested properties.
var a = {};
var b = {};
a.prop1 = 2;
a.prop2 = { prop3: 2 };
b.prop1 = 2;
b.prop2 = { prop3: 3 };
The object could be much more complex with more nested properties. But this one is a good example. I have the option to use recursive functions or something with lodash...

An easy and elegant solution is to use _.isEqual, which performs a deep comparison:
var a = {};
var b = {};
a.prop1 = 2;
a.prop2 = { prop3: 2 };
b.prop1 = 2;
b.prop2 = { prop3: 3 };
console.log(_.isEqual(a, b)); // returns false if different
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>
However, this solution doesn't show which property is different.

If you need to know which properties are different, use reduce():
_.reduce(a, function(result, value, key) {
return _.isEqual(value, b[key]) ?
result : result.concat(key);
}, []);
// → [ "prop2" ]

For anyone stumbling upon this thread, here's a more complete solution. It will compare two objects and give you the key of all properties that are either only in object1, only in object2, or are both in object1 and object2 but have different values:
/*
* Compare two objects by reducing an array of keys in obj1, having the
* keys in obj2 as the intial value of the result. Key points:
*
* - All keys of obj2 are initially in the result.
*
* - If the loop finds a key (from obj1, remember) not in obj2, it adds
* it to the result.
*
* - If the loop finds a key that are both in obj1 and obj2, it compares
* the value. If it's the same value, the key is removed from the result.
*/
function getObjectDiff(obj1, obj2) {
const diff = Object.keys(obj1).reduce((result, key) => {
if (!obj2.hasOwnProperty(key)) {
result.push(key);
} else if (_.isEqual(obj1[key], obj2[key])) {
const resultKeyIndex = result.indexOf(key);
result.splice(resultKeyIndex, 1);
}
return result;
}, Object.keys(obj2));
return diff;
}
Here's an example output:
// Test
let obj1 = {
a: 1,
b: 2,
c: { foo: 1, bar: 2},
d: { baz: 1, bat: 2 }
}
let obj2 = {
b: 2,
c: { foo: 1, bar: 'monkey'},
d: { baz: 1, bat: 2 }
e: 1
}
getObjectDiff(obj1, obj2)
// ["c", "e", "a"]
If you don't care about nested objects and want to skip lodash, you can substitute the _.isEqual for a normal value comparison, e.g. obj1[key] === obj2[key].

Based on the answer by Adam Boduch, I wrote this function which compares two objects in the deepest possible sense, returning paths that have different values as well as paths missing from one or the other object.
The code was not written with efficiency in mind, and improvements in that regard are most welcome, but here is the basic form:
var compare = function (a, b) {
var result = {
different: [],
missing_from_first: [],
missing_from_second: []
};
_.reduce(a, function (result, value, key) {
if (b.hasOwnProperty(key)) {
if (_.isEqual(value, b[key])) {
return result;
} else {
if (typeof (a[key]) != typeof ({}) || typeof (b[key]) != typeof ({})) {
//dead end.
result.different.push(key);
return result;
} else {
var deeper = compare(a[key], b[key]);
result.different = result.different.concat(_.map(deeper.different, (sub_path) => {
return key + "." + sub_path;
}));
result.missing_from_second = result.missing_from_second.concat(_.map(deeper.missing_from_second, (sub_path) => {
return key + "." + sub_path;
}));
result.missing_from_first = result.missing_from_first.concat(_.map(deeper.missing_from_first, (sub_path) => {
return key + "." + sub_path;
}));
return result;
}
}
} else {
result.missing_from_second.push(key);
return result;
}
}, result);
_.reduce(b, function (result, value, key) {
if (a.hasOwnProperty(key)) {
return result;
} else {
result.missing_from_first.push(key);
return result;
}
}, result);
return result;
}
You can try the code using this snippet (running in full page mode is recommended):
var compare = function (a, b) {
var result = {
different: [],
missing_from_first: [],
missing_from_second: []
};
_.reduce(a, function (result, value, key) {
if (b.hasOwnProperty(key)) {
if (_.isEqual(value, b[key])) {
return result;
} else {
if (typeof (a[key]) != typeof ({}) || typeof (b[key]) != typeof ({})) {
//dead end.
result.different.push(key);
return result;
} else {
var deeper = compare(a[key], b[key]);
result.different = result.different.concat(_.map(deeper.different, (sub_path) => {
return key + "." + sub_path;
}));
result.missing_from_second = result.missing_from_second.concat(_.map(deeper.missing_from_second, (sub_path) => {
return key + "." + sub_path;
}));
result.missing_from_first = result.missing_from_first.concat(_.map(deeper.missing_from_first, (sub_path) => {
return key + "." + sub_path;
}));
return result;
}
}
} else {
result.missing_from_second.push(key);
return result;
}
}, result);
_.reduce(b, function (result, value, key) {
if (a.hasOwnProperty(key)) {
return result;
} else {
result.missing_from_first.push(key);
return result;
}
}, result);
return result;
}
var a_editor = new JSONEditor($('#a')[0], {
name: 'a',
mode: 'code'
});
var b_editor = new JSONEditor($('#b')[0], {
name: 'b',
mode: 'code'
});
var a = {
same: 1,
different: 2,
missing_from_b: 3,
missing_nested_from_b: {
x: 1,
y: 2
},
nested: {
same: 1,
different: 2,
missing_from_b: 3
}
}
var b = {
same: 1,
different: 99,
missing_from_a: 3,
missing_nested_from_a: {
x: 1,
y: 2
},
nested: {
same: 1,
different: 99,
missing_from_a: 3
}
}
a_editor.set(a);
b_editor.set(b);
var result_editor = new JSONEditor($('#result')[0], {
name: 'result',
mode: 'view'
});
var do_compare = function() {
var a = a_editor.get();
var b = b_editor.get();
result_editor.set(compare(a, b));
}
#objects {} #objects section {
margin-bottom: 10px;
}
#objects section h1 {
background: #444;
color: white;
font-family: monospace;
display: inline-block;
margin: 0;
padding: 5px;
}
.jsoneditor-outer, .ace_editor {
min-height: 230px !important;
}
button:hover {
background: orangered;
}
button {
cursor: pointer;
background: red;
color: white;
text-align: left;
font-weight: bold;
border: 5px solid crimson;
outline: 0;
padding: 10px;
margin: 10px 0px;
}
<link href="https://cdnjs.cloudflare.com/ajax/libs/jsoneditor/5.5.10/jsoneditor.min.css" rel="stylesheet" />
<script src="https://cdnjs.cloudflare.com/ajax/libs/jsoneditor/5.5.10/jsoneditor.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="objects">
<section>
<h1>a (first object)</h1>
<div id="a"></div>
</section>
<section>
<h1>b (second object)</h1>
<div id="b"></div>
</section>
<button onClick="do_compare()">compare</button>
<section>
<h1>result</h1>
<div id="result"></div>
</section>
</div>

Here's a concise solution using Lodash:
_.differenceWith(a, b, _.isEqual);
Note both inputs need to be arrays (possibly an array of one object).

To recursively show how an object is different with other you can use _.reduce combined with _.isEqual and _.isPlainObject. In this case you can compare how a is different with b or how b is different with a:
const objectA = {
a: {
1: "SAME WILL BE MISSING IN RESULT",
2: "BBB",
3: [1, 2, 3]
},
b: "not",
c: "foo bar"
};
const objectB = {
a: {
1: "SAME WILL BE MISSING IN RESULT",
2: [1, 2]
},
b: "foo",
c: "bar"
};
const diff = function(obj1, obj2) {
return _.reduce(obj1, function(result, value, key) {
if (_.isPlainObject(value)) {
result[key] = diff(value, obj2[key]);
} else if (!_.isEqual(value, obj2[key])) {
result[key] = value;
}
return result;
}, {});
};
const diffAOverB = diff(objectA, objectB);
const diffBOverA = diff(objectA, objectB);
console.log(diffAOverB);
console.log(diffBOverA);
<script src="https://cdn.jsdelivr.net/npm/lodash#4.17.4/lodash.min.js"></script>

This code returns an object with all properties that have a different value and also values of both objects. Useful to logging the difference.
var allkeys = _.union(_.keys(obj1), _.keys(obj2));
var difference = _.reduce(allkeys, function (result, key) {
if ( !_.isEqual(obj1[key], obj2[key]) ) {
result[key] = {obj1: obj1[key], obj2: obj2[key]}
}
return result;
}, {});

Simple use _.isEqual method, it will work for all comparing...
Note: This method supports comparing arrays, array buffers,
booleans,
* date objects, error objects, maps, numbers, Object objects, regexes,
* sets, strings, symbols, and typed arrays. Object objects are compared
* by their own, not inherited, enumerable properties. Functions and DOM
* nodes are not supported.
So if you have below:
const firstName = {name: "Alireza"};
const otherName = {name: "Alireza"};
If you do: _.isEqual(firstName, otherName);,
it will return true
And if const fullName = {firstName: "Alireza", familyName: "Dezfoolian"};
If you do: _.isEqual(firstName, fullName);,
will return false

There have been many answers posted but for those curious to avoid writing any code to calculate difference between two objects having any type of structure there is actually a library to do this. Lodash isEqual only returns true or false it doesn't return any information about the changed properties. https://www.npmjs.com/package/deep-diff
its returns full detail of differences between two objects
import DeepDiff from 'deep-diff';
let a = {...} //some object
let b = {...} //some object
var differences = DeepDiff.diff(a, b);
Similar question has also been asked in this thread
Getting the difference between 2 JSON objects

I took a stab a Adam Boduch's code to output a deep diff - this is entirely untested but the pieces are there:
function diff (obj1, obj2, path) {
obj1 = obj1 || {};
obj2 = obj2 || {};
return _.reduce(obj1, function(result, value, key) {
var p = path ? path + '.' + key : key;
if (_.isObject(value)) {
var d = diff(value, obj2[key], p);
return d.length ? result.concat(d) : result;
}
return _.isEqual(value, obj2[key]) ? result : result.concat(p);
}, []);
}
diff({ foo: 'lol', bar: { baz: true }}, {}) // returns ["foo", "bar.baz"]

As it was asked, here's a recursive object comparison function. And a bit more. Assuming that primary use of such function is object inspection, I have something to say. Complete deep comparison is a bad idea when some differences are irrelevant. For example, blind deep comparison in TDD assertions makes tests unnecessary brittle. For that reason, I'd like to introduce a much more valuable partial diff. It is a recursive analogue of a previous contribution to this thread. It ignores keys not present in a
var bdiff = (a, b) =>
_.reduce(a, (res, val, key) =>
res.concat((_.isPlainObject(val) || _.isArray(val)) && b
? bdiff(val, b[key]).map(x => key + '.' + x)
: (!b || val != b[key] ? [key] : [])),
[]);
BDiff allows checking for expected values while tolerating other properties, which is exactly what you want for automatic inspection. This allows building all kinds of advanced assertions. For example:
var diff = bdiff(expected, actual);
// all expected properties match
console.assert(diff.length == 0, "Objects differ", diff, expected, actual);
// controlled inequality
console.assert(diff.length < 3, "Too many differences", diff, expected, actual);
Returning to the complete solution. Building a full traditional diff with bdiff is trivial:
function diff(a, b) {
var u = bdiff(a, b), v = bdiff(b, a);
return u.filter(x=>!v.includes(x)).map(x=>' < ' + x)
.concat(u.filter(x=>v.includes(x)).map(x=>' | ' + x))
.concat(v.filter(x=>!u.includes(x)).map(x=>' > ' + x));
};
Running above function on two complex objects will output something similar to this:
[
" < components.0.components.1.components.1.isNew",
" < components.0.cryptoKey",
" | components.0.components.2.components.2.components.2.FFT.min",
" | components.0.components.2.components.2.components.2.FFT.max",
" > components.0.components.1.components.1.merkleTree",
" > components.0.components.2.components.2.components.2.merkleTree",
" > components.0.components.3.FFTResult"
]
Finally, in order to have a glimpse into how the values differ, we may want to directly eval() the diff output. For that, we need an uglier version of bdiff that outputs syntactically correct paths:
// provides syntactically correct output
var bdiff = (a, b) =>
_.reduce(a, (res, val, key) =>
res.concat((_.isPlainObject(val) || _.isArray(val)) && b
? bdiff(val, b[key]).map(x =>
key + (key.trim ? '':']') + (x.search(/^\d/)? '.':'[') + x)
: (!b || val != b[key] ? [key + (key.trim ? '':']')] : [])),
[]);
// now we can eval output of the diff fuction that we left unchanged
diff(a, b).filter(x=>x[1] == '|').map(x=>[x].concat([a, b].map(y=>((z) =>eval('z.' + x.substr(3))).call(this, y)))));
That will output something similar to this:
[" | components[0].components[2].components[2].components[2].FFT.min", 0, 3]
[" | components[0].components[2].components[2].components[2].FFT.max", 100, 50]
MIT license ;)

Here is a simple Typescript with Lodash deep difference checker which will produce a new object with just the differences between an old object and a new object.
For example, if we had:
const oldData = {a: 1, b: 2};
const newData = {a: 1, b: 3};
the resulting object would be:
const result: {b: 3};
It is also compatible with multi-level deep objects, for arrays it may need some tweaking.
import * as _ from "lodash";
export const objectDeepDiff = (data: object | any, oldData: object | any) => {
const record: any = {};
Object.keys(data).forEach((key: string) => {
// Checks that isn't an object and isn't equal
if (!(typeof data[key] === "object" && _.isEqual(data[key], oldData[key]))) {
record[key] = data[key];
}
// If is an object, and the object isn't equal
if ((typeof data[key] === "object" && !_.isEqual(data[key], oldData[key]))) {
record[key] = objectDeepDiff(data[key], oldData[key]);
}
});
return record;
};

Deep compare using a template of (nested) properties to check
function objetcsDeepEqualByTemplate(objectA, objectB, comparisonTemplate) {
if (!objectA || !objectB) return false
let areDifferent = false
Object.keys(comparisonTemplate).some((key) => {
if (typeof comparisonTemplate[key] === 'object') {
areDifferent = !objetcsDeepEqualByTemplate(objectA[key], objectB[key], comparisonTemplate[key])
return areDifferent
} else if (comparisonTemplate[key] === true) {
areDifferent = objectA[key] !== objectB[key]
return areDifferent
} else {
return false
}
})
return !areDifferent
}
const objA = {
a: 1,
b: {
a: 21,
b: 22,
},
c: 3,
}
const objB = {
a: 1,
b: {
a: 21,
b: 25,
},
c: true,
}
// template tells which props to compare
const comparisonTemplateA = {
a: true,
b: {
a: true
}
}
objetcsDeepEqualByTemplate(objA, objB, comparisonTemplateA)
// returns true
const comparisonTemplateB = {
a: true,
c: true
}
// returns false
objetcsDeepEqualByTemplate(objA, objB, comparisonTemplateB)
This will work in the console. Array support could be added if needed

I need to know if they have difference in one of their nested properties
Other answers provide potentially satisfactory solutions to this problem, but it is sufficiently difficult and common that it looks like there's a very popular package to help solve this issue deep-object-diff.
To use this package you'd need to npm i deep-object-diff then:
const { diff } = require('deep-object-diff');
var a = {};
var b = {};
a.prop1 = 2;
a.prop2 = { prop3: 2 };
b.prop1 = 2;
b.prop2 = { prop3: 3 };
if (!_.isEqual(a, b)) {
const abDiff = diff(a, b);
console.log(abDiff);
/*
{
prop2: {
prop3: 3
}
}
*/
}
// or alternatively
const abDiff = diff(a, b);
if(!_.isEmpty(abDiff)) {
// if a diff exists then they aren't deeply equal
// perform needed actions with diff...
}
Here's a more detailed case with property deletions directly from their docs:
const lhs = {
foo: {
bar: {
a: ['a', 'b'],
b: 2,
c: ['x', 'y'],
e: 100 // deleted
}
},
buzz: 'world'
};
const rhs = {
foo: {
bar: {
a: ['a'], // index 1 ('b') deleted
b: 2, // unchanged
c: ['x', 'y', 'z'], // 'z' added
d: 'Hello, world!' // added
}
},
buzz: 'fizz' // updated
};
console.log(diff(lhs, rhs)); // =>
/*
{
foo: {
bar: {
a: {
'1': undefined
},
c: {
'2': 'z'
},
d: 'Hello, world!',
e: undefined
}
},
buzz: 'fizz'
}
*/
For implementation details and other usage info, refer to that repo.

I know this doesn't directly answer the OP's question but I was led here by searching for how to remove lodash. So hopefully this helps someone else in a similar position as me.
Credit goes to #JohanPersson. I built off of that answer to implement comparing deeply nested values and getting the key reference to the diffs
getObjectDiff = (obj1, obj2) => {
const obj1Props = Object.keys(obj1);
const obj2Props = Object.keys(obj2);
const keysWithDiffValue = obj1Props.reduce((keysWithDiffValueAccumulator, key) => {
const propExistsOnObj2 = obj2.hasOwnProperty(key);
const hasNestedValue = obj1[key] instanceof Object && obj2[key] instanceof Object;
const keyValuePairBetweenBothObjectsIsEqual = obj1[key] === obj2[key];
if (!propExistsOnObj2) {
keysWithDiffValueAccumulator.push(key);
} else if (hasNestedValue) {
const keyIndex = keysWithDiffValueAccumulator.indexOf(key);
if (keyIndex >= 0) {
keysWithDiffValueAccumulator.splice(keyIndex, 1);
}
const nestedDiffs = getObjectDiff(obj1[key], obj2[key]);
for (let diff of nestedDiffs) {
keysWithDiffValueAccumulator.push(`${key}.${diff}`);
}
} else if (keyValuePairBetweenBothObjectsIsEqual) {
const equalValueKeyIndex = keysWithDiffValueAccumulator.indexOf(key);
keysWithDiffValueAccumulator.splice(equalValueKeyIndex, 1);
}
return keysWithDiffValueAccumulator;
}, obj2Props);
return keysWithDiffValue;
}
const obj1 = {a0: {a1: {a2: {a3: 'Im here'}}}};
const obj2 = {a0: {a1: {a2: {a3: 'Not here', b3: 'some'}}}};
console.log('final', getObjectDiff(obj1, obj2));

Without use of lodash/underscore, I have written this code and is working fine for me for a deep comparison of object1 with object2
function getObjectDiff(a, b) {
var diffObj = {};
if (Array.isArray(a)) {
a.forEach(function(elem, index) {
if (!Array.isArray(diffObj)) {
diffObj = [];
}
diffObj[index] = getObjectDiff(elem, (b || [])[index]);
});
} else if (a != null && typeof a == 'object') {
Object.keys(a).forEach(function(key) {
if (Array.isArray(a[key])) {
var arr = getObjectDiff(a[key], b[key]);
if (!Array.isArray(arr)) {
arr = [];
}
arr.forEach(function(elem, index) {
if (!Array.isArray(diffObj[key])) {
diffObj[key] = [];
}
diffObj[key][index] = elem;
});
} else if (typeof a[key] == 'object') {
diffObj[key] = getObjectDiff(a[key], b[key]);
} else if (a[key] != (b || {})[key]) {
diffObj[key] = a[key];
} else if (a[key] == (b || {})[key]) {
delete a[key];
}
});
}
Object.keys(diffObj).forEach(function(key) {
if (typeof diffObj[key] == 'object' && JSON.stringify(diffObj[key]) == '{}') {
delete diffObj[key];
}
});
return diffObj;
}

This is my solution to the problem
const _ = require('lodash');
var objects = [{ 'x': 1, 'y': 2, 'z':3, a:{b:1, c:2, d:{n:0}}, p:[1, 2, 3] }, { 'x': 2, 'y': 1, z:3, a:{b:2, c:2,d:{n:1}}, p:[1,3], m:3 }];
const diffFn=(a,b, path='')=>_.reduce(a, function(result, value, key) {
if(_.isObjectLike(value)){
if(_.isEqual(value, b[key])){
return result;
}else{
return result.concat(diffFn(value, b[key], path?(`${path}.${key}`):key))
}
}else{
return _.isEqual(value, b[key]) ?
result : result.concat(path?(`${path}.${key}`):key);
}
}, []);
const diffKeys1=diffFn(objects[0], objects[1])
const diffKeys2=diffFn(objects[1], objects[0])
const diffKeys=_.union(diffKeys1, diffKeys2)
const res={};
_.forEach(diffKeys, (key)=>_.assign(res, {[key]:{ old: _.get(objects[0], key), new:_.get(objects[1], key)} }))
res
/*
Returns
{
x: { old: 1, new: 2 },
y: { old: 2, new: 1 },
'a.b': { old: 1, new: 2 },
'a.d.n': { old: 0, new: 1 },
'p.1': { old: 2, new: 3 },
'p.2': { old: 3, new: undefined },
m: { old: undefined, new: 3 }
}
*/

Completing the answer from Adam Boduch, this one takes into differences in properties
const differenceOfKeys = (...objects) =>
_.difference(...objects.map(obj => Object.keys(obj)));
const differenceObj = (a, b) =>
_.reduce(a, (result, value, key) => (
_.isEqual(value, b[key]) ? result : [...result, key]
), differenceOfKeys(b, a));

If you need only key comparison:
_.reduce(a, function(result, value, key) {
return b[key] === undefined ? key : []
}, []);

We had this requirement on getting the delta between two json updates for tracking database updates. Maybe someone else can find this helpful.
https://gist.github.com/jp6rt/7fcb6907e159d7851c8d59840b669e3d
const {
isObject,
isEqual,
transform,
has,
merge,
} = require('lodash');
const assert = require('assert');
/**
* Perform a symmetric comparison on JSON object.
* #param {*} baseObj - The base object to be used for comparison against the withObj.
* #param {*} withObj - The withObject parameter is used as the comparison on the base object.
* #param {*} invert - Because this is a symmetric comparison. Some values in the with object
* that doesn't exist on the base will be lost in translation.
* You can execute again the function again with the parameters interchanged.
* However you will lose the reference if the value is from the base or with
* object if you intended to do an assymetric comparison.
* Setting this to true will do make sure the reference is not lost.
* #returns - The returned object will label the result of the comparison with the
* value from base and with object.
*/
const diffSym = (baseObj, withObj, invert = false) => transform(baseObj, (result, value, key) => {
if (isEqual(value, withObj[key])
&& has(withObj, key)) {
return;
}
if (isObject(value)
&& isObject(withObj[key])
&& !Array.isArray(value)) {
result[key] = diffSym(value, withObj[key], invert);
return;
}
if (!invert) {
result[key] = {
base: value,
with: withObj[key],
};
return;
}
if (invert) {
result[key] = {
base: withObj[key],
with: value,
};
}
});
/**
* Perform a assymmetric comparison on JSON object.
* #param {*} baseObj - The base object to be used for comparison against the withObj.
* #param {*} withObj - The withObject parameter is used as the comparison on the base object.
* #returns - The returned object will label the values with
* reference to the base and with object.
*/
const diffJSON = (baseObj, withObj) => {
// Deep clone the objects so we don't update the reference objects.
const baseObjClone = JSON.parse(JSON.stringify(baseObj));
const withObjClone = JSON.parse(JSON.stringify(withObj));
const beforeDelta = diffSym(baseObjClone, withObjClone);
const afterDelta = diffSym(withObjClone, baseObjClone, true);
return merge(afterDelta, beforeDelta);
};
// By Example:
const beforeDataObj = {
a: 1,
c: { d: 2, f: 3 },
g: 4,
h: 5,
};
const afterDataObj = {
a: 2,
b: 3,
c: { d: 1, e: 1 },
h: 5,
};
const delta = diffJSON(beforeDataObj, afterDataObj);
// Assert expected result.
assert(isEqual(delta, {
a: { base: 1, with: 2 },
b: { base: undefined, with: 3 },
c: {
d: { base: 2, with: 1 },
e: { base: undefined, with: 1 },
f: { base: 3, with: undefined },
},
g: { base: 4, with: undefined },
}));

This solution returns an object with the modified attributes.
_.reduce(a, (r, v, k) => { return _.merge(r, _.isEqual(v, b[k]) ? {} : { [k]: v }); }, {});

var isEqual = function(f,s) {
if (f === s) return true;
if (Array.isArray(f)&&Array.isArray(s)) {
return isEqual(f.sort(), s.sort());
}
if (_.isObject(f)) {
return isEqual(f, s);
}
return _.isEqual(f, s);
};

this was based on #JLavoie, using lodash
let differences = function (newObj, oldObj) {
return _.reduce(newObj, function (result, value, key) {
if (!_.isEqual(value, oldObj[key])) {
if (_.isArray(value)) {
result[key] = []
_.forEach(value, function (innerObjFrom1, index) {
if (_.isNil(oldObj[key][index])) {
result[key].push(innerObjFrom1)
} else {
let changes = differences(innerObjFrom1, oldObj[key][index])
if (!_.isEmpty(changes)) {
result[key].push(changes)
}
}
})
} else if (_.isObject(value)) {
result[key] = differences(value, oldObj[key])
} else {
result[key] = value
}
}
return result
}, {})
}
https://jsfiddle.net/EmilianoBarboza/0g0sn3b9/8/

To build upon Sridhar Gudimela's answer, here it is updated in a way that uses TypeScript:
/// U T I L S
interface LooseObjectInterface {
[key: string]: any;
};
type inputOptions = LooseObjectInterface | any[];
/// E X P O R T
export const objectCompare = (objectA: inputOptions, objectB: inputOptions): LooseObjectInterface => {
let diffObj: LooseObjectInterface = {};
switch(true) {
case (Array.isArray(objectA)):
objectA.forEach((elem: any, index: number) => {
if (!Array.isArray(diffObj))
diffObj = [];
diffObj[index] = objectCompare(elem, (objectB || [])[index]);
});
break;
case (objectA !== null && typeof objectA === "object"):
Object.keys(objectA).forEach((key: any) => {
if (Array.isArray(objectA[key])) {
let arr = objectCompare(objectA[key], objectB[key]);
if (!Array.isArray(arr))
arr = [];
arr.forEach((elem: any, index: number) => {
if (!Array.isArray(diffObj[key]))
diffObj[key] = [];
diffObj[key][index] = elem;
});
} else if (typeof objectA[key] === "object")
diffObj[key] = objectCompare(objectA[key], objectB[key]);
else if (objectA[key] !== (objectB || {})[key])
diffObj[key] = objectA[key];
else if (objectA[key] === (objectB || {})[key])
delete objectA[key];
});
break;
default:
break;
}
Object.keys(diffObj).forEach((key: any) => {
if (typeof diffObj[key] === "object" && JSON.stringify(diffObj[key]) === "{}")
delete diffObj[key];
});
return diffObj;
};
EDIT: My original answer used Flow, hence the downvotes (I assume, or maybe because my answer didn't use Lodash...however, having an answer to a similar problem can't hurt).

Efficiently rename/re-map javascript/json object keys within array of objects

I have some structured JSON data like so. Let's assume this is interchangeable, via JSON.parse():
[
{
"title": "pineapple",
"uid": "ab982d34c98f"
},
{
"title": "carrots",
"uid": "6f12e6ba45ec"
}
]
I need it to look like this, remapping title to name, and uid to id with the result:
[
{
"name": "pineapple",
"id": "ab982d34c98f"
},
{
"name": "carrots",
"id": "6f12e6ba45ec"
}
]
The most obvious way of doing it is like this:
str = '[{"title": "pineapple","uid": "ab982d34c98f"},{"title": "carrots", "uid": "6f12e6ba45ec"}]';
var arr = JSON.parse(str);
for (var i = 0; i<arr.length; i++) {
arr[i].name = arr[i].title;
arr[i].id = arr[i].uid;
delete arr[i].title;
delete arr[i].uid;
}
str = '[{"title": "pineapple","uid": "ab982d34c98f"},{"title": "carrots", "uid": "6f12e6ba45ec"}]';
var arr = JSON.parse(str);
for (var i = 0; i<arr.length; i++) {
arr[i].name = arr[i].title;
arr[i].id = arr[i].uid;
delete arr[i].title;
delete arr[i].uid;
}
$('body').append("<pre>"+JSON.stringify(arr, undefined, 4)+"</pre>");
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
...or using something more complex (albeit not more efficient) like this.
This is all fine and dandy, but what if there were 200,000 objects in the array? This is a lot of processing overhead.
Is there a more efficient way to remap a key name? Possibly without looping through the entire array of objects? If your method is more efficient, please provide proof/references.

As I already mentioned in the comments, if you can make certain assumptions about the values of the objects, you could use a regular expression to replace the keys, for example:
str = str.replace(/"title":/g, '"name":');
It's not as "clean", but it might get the job done faster.
If you have to parse the JSON anyway, a more structured approach would be to pass a reviver function to JSON.parse and you might be able to avoid an additional pass over the array. This probably depends on how engine implement JSON.parse though (maybe they parse the whole string first and then make a second pass with the reviver function, in which case you wouldn't get any advantage).
var arr = JSON.parse(str, function(prop, value) {
switch(prop) {
case "title":
this.name = value;
return;
case "uid":
this.id = value;
return;
default:
return value;
}
});
Benchmarks, using the Node.js script below to test 3 times:
1389822740739: Beginning regex rename test
1389822740761: Regex rename complete
// 22ms, 22ms, 21ms
1389822740762: Beginning parse and remap in for loop test
1389822740831: For loop remap complete
// 69ms, 68ms, 68ms
1389822740831: Beginning reviver function test
1389822740893: Reviver function complete
// 62ms, 61ms, 60ms
It appears as if the regex (in this case) is the most efficient, but be careful when trying to parse JSON with regular expressions.
Test script, loading 100,230 lines of the OP's sample JSON:
fs = require('fs');
fs.readFile('test.json', 'utf8', function (err, data) {
if (err) {
return console.log(err);
}
console.log(new Date().getTime() + ": Beginning regex rename test");
var str = data.replace(/"title":/g, '"name":');
str = str.replace(/"uid":/g, '"id":');
JSON.parse(str);
console.log(new Date().getTime() + ": Regex rename complete");
console.log(new Date().getTime() + ": Beginning parse and remap in for loop test");
var arr = JSON.parse(data);
for (var i = 0; i < arr.length; i++) {
arr[i].name = arr[i].title;
arr[i].id = arr[i].uid;
delete arr[i].title;
delete arr[i].uid;
}
console.log(new Date().getTime() + ": For loop remap complete");
console.log(new Date().getTime() + ": Beginning reviver function test");
var arr = JSON.parse(data, function (prop, value) {
switch (prop) {
case "title":
this.name = value;
return;
case "uid":
this.id = value;
return;
default:
return value;
}
});
console.log(new Date().getTime() + ": Reviver function complete");
});

Asked this question a long time ago, and since then, I've grown acustomed to using Array.prototype.map() to get the job done, more for stability and cleanliness of code than performance. While it's certainly not the most performant, it looks great:
var repl = orig.map(function(obj) {
return {
name: obj.title,
id: obj.uid
}
})
If you need a more flexible (and ES6-compatible function), try:
let replaceKeyInObjectArray = (a, r) => a.map(o =>
Object.keys(o).map((key) => ({ [r[key] || key] : o[key] })
).reduce((a, b) => Object.assign({}, a, b)))
e.g.
const arr = [{ abc: 1, def: 40, xyz: 50 }, { abc: 1, def: 40, xyz: 50 }, { abc: 1, def: 40, xyz: 50 }]
const replaceMap = { "abc": "yyj" }
replaceKeyInObjectArray(arr, replaceMap)
/*
[
{
"yyj": 1,
"def": 40,
"xyz": 50
},
{
"yyj": 1,
"def": 40,
"xyz": 50
},
{
"yyj": 1,
"def": 40,
"xyz": 50
}
]
*/

Here's another take on the OP's suggestion to use map() for clarity (not performance).
var newItems = items.map(item => ({
name: item.title,
id: item.uid
}));
This uses ES6 arrow functions and the shortcut syntaxes that are possible when there's only one parm passed to the function and only one statement in the body of the function.
Depending on your history with lambda expressions in various languages, this form may or may not resonate with you.
Be careful when returning an object literal in the arrow function shortcut syntax like this. Don't forget the additional parens around the object literal!

If you want to make it a little more reusable. Maybe this is a decent approach.
function rekey(arr, lookup) {
for (var i = 0; i < arr.length; i++) {
var obj = arr[i];
for (var fromKey in lookup) {
var toKey = lookup[fromKey];
var value = obj[fromKey];
if (value) {
obj[toKey] = value;
delete obj[fromKey];
}
}
}
return arr;
}
var arr = [{ apple: 'bar' }, { apple: 'foo' }];
var converted = rekey(arr, { apple: 'kung' });
console.log(converted);

Using ES6:
const renameFieldInArrayOfObjects = (arr, oldField, newField) => {
return arr.map(s => {
return Object.keys(s).reduce((prev, next) => {
if(next === oldField) {
prev[newField] = s[next]
} else {
prev[next] = s[next]
}
return prev
}, {})
})
}
Using ES7:
const renameFieldInArrayOfObjects = (arr, oldField, newField) => {
return arr.map(s => {
return Object.keys(s).reduce((prev, next) => {
return next === oldField
? {...prev, [newField]: s[next]}
: {...prev, [next]: s[next]}
}, {})
})
}

You can use an npm package named node-data-transform.
Your data :
const data = [
{
title: 'pineapple',
uid: 'ab982d34c98f',
},
{
title: 'carrots',
uid: '6f12e6ba45ec',
},
];
Your mapping :
const map = {
item: {
name: 'title',
id: 'uid',
},
};
And use the package :
const DataTransform = require("node-json-transform").DataTransform;
const dataTransform = DataTransform(data, map);
const result = dataTransform.transform();
console.log(result);
Result :
[
{
name: 'pineapple',
id: 'ab982d34c98f'
},
{
name: 'carrots',
id: '6f12e6ba45ec'
}
]
Maybe it's not the best way for performance, but it's quite elegant.

var jsonObj = [/*sample array in question*/ ]
Based on different benchmarks discussed below, fastest solution is native for:
var arr = [];
for(var i = 0, len = jsonObj .length; i < len; i++) {
arr.push( {"name": jsonObj[i].title, "id" : jsonObj[i].uid});
}
I think alternatively without using a frameworks this will be option 2:
var arr = []
jsonObj.forEach(function(item) { arr.push({"name": item.title, "id" : item.uid }); });
There is always debate between using navite and non-navite functions. If I remember correctly lodash argued they were faster than underscore because the use non-native functions for key operations.
However different browsers will produce sometimes very different results. I always looked for the best average.
For benchmarks you can take a look at this:
http://jsperf.com/lo-dash-v1-1-1-vs-underscore-v1-4-4/8

function replaceElem(value, replace, str) {
while (str.indexOf(value) > -1) {
str = str.replace(value, replace);
}
return str;
}
call this from main
var value = "tittle";
var replace = "name";
replaceElem(value, replace, str);

Find property by name in a deep object

I have a HUGE collection and I am looking for a property by key someplace inside the collection. What is a reliable way to get a list of references or full paths to all objects containing that key/index? I use jQuery and lodash if it helps and you can forget about infinite pointer recursion, this is a pure JSON response.
fn({ 'a': 1, 'b': 2, 'c': {'d':{'e':7}}}, "d");
// [o.c]
fn({ 'a': 1, 'b': 2, 'c': {'d':{'e':7}}}, "e");
// [o.c.d]
fn({ 'aa': 1, 'bb': 2, 'cc': {'d':{'x':9}}, dd:{'d':{'y':9}}}, 'd');
// [o.cc,o.cc.dd]
fwiw lodash has a _.find function that will find nested objects that are two nests deep, but it seems to fail after that. (e.g. http://codepen.io/anon/pen/bnqyh)

This should do it:
function fn(obj, key) {
if (_.has(obj, key)) // or just (key in obj)
return [obj];
// elegant:
return _.flatten(_.map(obj, function(v) {
return typeof v == "object" ? fn(v, key) : [];
}), true);
// or efficient:
var res = [];
_.forEach(obj, function(v) {
if (typeof v == "object" && (v = fn(v, key)).length)
res.push.apply(res, v);
});
return res;
}

a pure JavaScript solution would look like the following:
function findNested(obj, key, memo) {
var i,
proto = Object.prototype,
ts = proto.toString,
hasOwn = proto.hasOwnProperty.bind(obj);
if ('[object Array]' !== ts.call(memo)) memo = [];
for (i in obj) {
if (hasOwn(i)) {
if (i === key) {
memo.push(obj[i]);
} else if ('[object Array]' === ts.call(obj[i]) || '[object Object]' === ts.call(obj[i])) {
findNested(obj[i], key, memo);
}
}
}
return memo;
}
here's how you'd use this function:
findNested({'aa': 1, 'bb': 2, 'cc': {'d':{'x':9}}, dd:{'d':{'y':9}}}, 'd');
and the result would be:
[{x: 9}, {y: 9}]

this will deep search an array of objects (hay) for a value (needle) then return an array with the results...
search = function(hay, needle, accumulator) {
var accumulator = accumulator || [];
if (typeof hay == 'object') {
for (var i in hay) {
search(hay[i], needle, accumulator) == true ? accumulator.push(hay) : 1;
}
}
return new RegExp(needle).test(hay) || accumulator;
}

If you can write a recursive function in plain JS (or with combination of lodash) that will be the best one (by performance), but if you want skip recursion from your side and want to go for a simple readable code (which may not be best as per performance) then you can use lodash#cloneDeepWith for any purposes where you have to traverse a object recursively.
let findValuesDeepByKey = (obj, key, res = []) => (
_.cloneDeepWith(obj, (v,k) => {k==key && res.push(v)}) && res
)
So, the callback you passes as the 2nd argument of _.cloneDeepWith will recursively traverse all the key/value pairs recursively and all you have to do is the operation you want to do with each. the above code is just a example of your case. Here is a working example:
var object = {
prop1: 'ABC1',
prop2: 'ABC2',
prop3: {
prop4: 'ABC3',
prop5Arr: [{
prop5: 'XYZ'
},
{
prop5: 'ABC4'
},
{
prop6: {
prop6NestedArr: [{
prop1: 'XYZ Nested Arr'
},
{
propFurtherNested: {key100: '100 Value'}
}
]
}
}
]
}
}
let findValuesDeepByKey = (obj, key, res = []) => (
_.cloneDeepWith(obj, (v,k) => {k==key && res.push(v)}) && res
)
console.log(findValuesDeepByKey(object, 'prop1'));
console.log(findValuesDeepByKey(object, 'prop5'));
console.log(findValuesDeepByKey(object, 'key100'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>

With Deepdash you can pickDeep and then get paths from it, or indexate (build path->value object)
var obj = { 'aa': 1, 'bb': 2, 'cc': {'d':{'x':9}}, dd:{'d':{'y':9}}}
var cherry = _.pickDeep(obj,"d");
console.log(JSON.stringify(cherry));
// {"cc":{"d":{}},"dd":{"d":{}}}
var paths = _.paths(cherry);
console.log(paths);
// ["cc.d", "dd.d"]
paths = _.paths(cherry,{pathFormat:'array'});
console.log(JSON.stringify(paths));
// [["cc","d"],["dd","d"]]
var index = _.indexate(cherry);
console.log(JSON.stringify(index));
// {"cc.d":{},"dd.d":{}}
Here is a Codepen demo

Something like this would work, converting it to an object and recursing down.
function find(jsonStr, searchkey) {
var jsObj = JSON.parse(jsonStr);
var set = [];
function fn(obj, key, path) {
for (var prop in obj) {
if (prop === key) {
set.push(path + "." + prop);
}
if (obj[prop]) {
fn(obj[prop], key, path + "." + prop);
}
}
return set;
}
fn(jsObj, searchkey, "o");
}
Fiddle: jsfiddle

In case you don't see the updated answer from #eugene, this tweak allows for passing a list of Keys to search for!
// Method that will find any "message" in the Apex errors that come back after insert attempts
// Could be a validation rule, or duplicate record, or pagemessage.. who knows!
// Use in your next error toast from a wire or imperative catch path!
// message: JSON.stringify(this.findNested(error, ['message', 'stackTrace'])),
// Testing multiple keys: this.findNested({thing: 0, list: [{message: 'm'}, {stackTrace: 'st'}], message: 'm2'}, ['message', 'stackTrace'])
findNested(obj, keys, memo) {
let i,
proto = Object.prototype,
ts = proto.toString,
hasOwn = proto.hasOwnProperty.bind(obj);
if ('[object Array]' !== ts.call(memo)) memo = [];
for (i in obj) {
if (hasOwn(i)) {
if (keys.includes(i)) {
memo.push(obj[i]);
} else if ('[object Array]' === ts.call(obj[i]) || '[object Object]' === ts.call(obj[i])) {
this.findNested(obj[i], keys, memo);
}
}
}
return memo.length == 0 ? null : memo;
}

Here's how I did it:
function _find( obj, field, results )
{
var tokens = field.split( '.' );
// if this is an array, recursively call for each row in the array
if( obj instanceof Array )
{
obj.forEach( function( row )
{
_find( row, field, results );
} );
}
else
{
// if obj contains the field
if( obj[ tokens[ 0 ] ] !== undefined )
{
// if we're at the end of the dot path
if( tokens.length === 1 )
{
results.push( obj[ tokens[ 0 ] ] );
}
else
{
// keep going down the dot path
_find( obj[ tokens[ 0 ] ], field.substr( field.indexOf( '.' ) + 1 ), results );
}
}
}
}
Testing it with:
var obj = {
document: {
payload: {
items:[
{field1: 123},
{field1: 456}
]
}
}
};
var results = [];
_find(obj.document,'payload.items.field1', results);
console.log(results);
Outputs
[ 123, 456 ]

We use object-scan for data processing tasks. It's pretty awesome once you've wrapped your head around how to use it.
// const objectScan = require('object-scan');
const haystack = { a: { b: { c: 'd' }, e: { f: 'g' } } };
const r = objectScan(['a.*.*'], { joined: true, rtn: 'entry' })(haystack);
console.log(r);
// => [ [ 'a.e.f', 'g' ], [ 'a.b.c', 'd' ] ]
.as-console-wrapper {max-height: 100% !important; top: 0}
<script src="https://bundle.run/object-scan#13.8.0"></script>
Disclaimer: I'm the author of object-scan
There are plenty more examples on the website.

The shortest and simplest solution:
Array.prototype.findpath = function(item,path) {
return this.find(function(f){return item==eval('f.'+path)});
}

Can one set multiple properties inside an object literal to the same value?

For example, can I do this?:
{
a: b: c: d: 1,
e: 2,
geh: function() { alert("Hi!") }
}
EDIT:
Is there some way I can avoid doing this?:
{
a: 1,
b: 1,
c: 1,
d: 1,
e: 2,
geh: function() { alert("Hi!") }
}

An update to this (in terms of the latest JavaScript abilities) avoiding unwanted defined vars:
{
let v;
var obj = {
"a": (v = 'some value'),
"b": v,
"c": v
};
}
This will mean v won't be defined outside the block, but obj will be.
Original answer
Another way of doing the same thing is:
var v;
var obj = {
"a": (v = 'some value'),
"b": v,
"c": v
};

You could set a line of equality between various properties:
var foo = {};
foo.a = foo.b = foo.c = "Hello";
Or you could just create a method that does the mass-assignment for you:
var foo = {
setValue: function( props, value ) {
while ( props.length ) this[ props.pop() ] = value;
}
}
foo.setValue( [ "a", "b", "c" ] , "Foo" );

You could try this. It's not the syntactic sugar you're looking for (eg. {a,b,c:1, d:2}) but it's another way to do it, although all of these answers are pretty much fine.
(object,fields,value)=>Object.assign(object||{}, ...fields.map(f=>({[f]:value}) ))
Explanation:
(object,fields,value)=>
Takes an object (or falsey value if you want a new object, feel free to rearrange the argument order)
Object.assign(object||{},
Will return an object based on object and it will mutate the object. To disable this, simply add a first argument object literal like this Object.assign({}, object || {}, ...
...fields.map(f=>({[f]:value}) )
Will spread the array of fields mapped to objects as a list of extra arguments to Object.assign. ['a','b'].map(f=>({[f]:value}) ) will give [{a:value}, {b:value}] and f(...[{a:1},{b:1}]) is like f({a:1},{b:1}). Object.assign does the rest :)

There's yet another approach: using a mapping function...
// This will be standard!
if (!Object.fromEntries)
Object.fromEntries = entries => entries.reduce ((o, [key, value]) => ({
...o,
[key]: value
}), {})
const setSameValue = (source, props, value) => ({
...source,
...Object.fromEntries (
props.map (prop => [prop, value])
)
})
// The important part: do what you want with ease!
const output = setSameValue ({}, ['1', '01'], 'string 1')
const obj = { x: 1, y: 'hello' }
const output2 = setSameValue (obj, ['1', '01'], 'string1')
console.log ('output1:', output)
console.log ('output2:', output2)

You could wrap in a closure too, if you didn't want multiple local vars. This syntax seems to be popular (but ugly):
var obj = (function() { var v='some value'; return { a:v, b:v, c:v }; })();

Use for of loop instead.
for (let [key, value] of Object.entries(object_name)) {
object_name[key] = 0; // the value that you want to assign
}

Or yet another way:
{...['a', 'b', 'c', 'd'].reduce((obj,prop)=>({...obj, [prop]: 1}), {}) }
It can be wrapped up pretty neatly by extending the Array prototype:
Array.prototype.ditto = function(v) { return this.reduce((o,p)=>({...o, [p]: v}), {}) }
So now it can be used like this:
{
...['a', 'b', 'c', 'd'].ditto(1),
...['e', 'f'].ditto(2)
geh: function() { alert("Hi!") }
}
Explanation: the .reduce starts off with an empty object {} and for each element prop return an object which is whatever was in the object already ...obj plus a new property with our value 1: [prop]: 1. Then expand these properties into the outer object with the ... at the start.
If you had tons of properties reduce wouldn't be the most efficient, but you could change it to:
Array.prototype.ditto = function(v) { let o = {}; this.forEach(p => o[p] = v); return o; }
More readable and more efficient but less cool??