Get all unique object properties from array of objects

You can use Object.assign() and spread syntax to merge the array of objects to a single object. Then get the keys from the merged object:

Object.keys(Object.assign({}, ...array)) 

Here's a snippet:

const array = [{firstName:"John",lastName:"Doe"},{firstName:"Anna",car:true},{firstName:"Peter",lastName:"Jones"}],
      unique = Object.keys(Object.assign({}, ...array))

console.log(unique)

Another option is to use Object.keys as callback to flatMap. This returns an array of all the keys. Then, create a Set to get unique keys and use Array.from() to convert the set to an array.

const keys = input.flatMap(Object.keys),
      unique = Array.from(new Set(keys));

Here's a working snippet:

const input=[{firstName:"John",lastName:"Doe"},{firstName:"Anna",car:true},{firstName:"Peter",lastName:"Jones"}],
      unique = Array.from(new Set(input.flatMap(Object.keys)));

console.log(unique)

If flatMap is not supported, you can use

const keys = [].concat(...input.map(Object.keys)),

You could use map() and keys() to return keys of each object and then union() and flatten()

var data = [{
  "firstName": "John",
  "lastName": "Doe"
}, {
  "firstName": "Anna",
  "car": true
}, {
  "firstName": "Peter",
  "lastName": "Jones"
}]

var result = _.union(_.flatten(_.map(data, (e) => _.keys(e))));
console.log(result)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.15.0/lodash.min.js"></script>

A solution using only:

• Object.assign
• Object.keys
• Array.prototype.reduce

var data = [{
  "firstName": "John",
  "lastName": "Doe"
}, {
  "firstName": "Anna",
  "car": true
}, {
  "firstName": "Peter",
  "lastName": "Jones"
}];

var uniqueKeys = Object.keys(data.reduce(function(result, obj) {
  return Object.assign(result, obj);
}, {}))

console.log(uniqueKeys);