javascript - Get unique keys from multiple objects

Question

If I have an array of objects like this:

var mountains = [
    { name: 'Kebnekaise', elevation: 2106 },
    { name: 'Mount Ngauruhoe', elevation: 2291, comment: 'aka Mount Doom' }
];

How to get all unique keys i.e. ['name', 'elevation', 'comment']?

Answer 1

In ECMAScript 2015, it's really simple:

let mountains = [
  { name: 'Kebnekaise', elevation: 2106 },
  { name: 'Mount Ngauruhoe', elevation: 2291, comment: 'aka Mount Doom' }
];

let uniqueKeys = Object.keys(Object.assign({}, ...mountains));