Best way to get intersection of keys of two objects?

Question

I have two object literals like so:

var firstObject = {     x: 0,     y: 1,     z: 2,      a: 10,     b: 20,     e: 30 }  var secondObject = {     x: 0,     y: 1,     z: 2,      a: 10,     c: 20,     d: 30 } 

I want to get the intersection of the keys these two object literals have like so:

var intersectionKeys  = ['x', 'y', 'z', 'a'] 

I can obviously do a loop and see if a key with the same name exists in the other object, but I am wondering if this would be a good case for some functional programming and map / filter / reduce usage? I myself have not done that much functional programming, but I have a feeling, that there could exist a clean and clever solution for this problem.

Answer 1

A solution without indexOf.

var firstObject = { x: 0, y: 1, z: 2, a: 10, b: 20, e: 30 },      secondObject = { x: 0, y: 1, z: 2, a: 10, c: 20, d: 30 };    function intersection(o1, o2) {      return Object.keys(o1).concat(Object.keys(o2)).sort().reduce(function (r, a, i, aa) {          if (i && aa[i - 1] === a) {              r.push(a);          }          return r;      }, []);  }    document.write('<pre>' + JSON.stringify(intersection(firstObject, secondObject), 0, 4) + '</pre>');

Second attempt with O(n).

var firstObject = { x: 0, y: 1, z: 2, a: 10, b: 20, e: 30 },      secondObject = { x: 0, y: 1, z: 2, a: 10, c: 20, d: 30 };    function intersection(o1, o2) {      return Object.keys(o1).filter({}.hasOwnProperty.bind(o2));  }    document.write('<pre>' + JSON.stringify(intersection(firstObject, secondObject), 0, 4) + '</pre>');