unionKeys

Obtain keys present in any map.

Similar: unionKeys, intersectionKeys.
Similar: union, intersection, difference, symmetricDifference, isDisjoint.

function unionKeys(...xs)
// xs: maps

const map = require('extra-map');

var x = new Map([['a', 1],  ['b', 2],  ['c', 3], ['d', 4]]);
var y = new Map([['b', 20], ['c', 30], ['e', 50]]);
map.unionKeys(x, y);
// → Set(5) { 'a', 'b', 'c', 'd', 'e' }

References

• Data.Set.union: Haskell
• Set.union: Python
• _.union: lodash
• _.unionBy: lodash
• _.unionWith: lodash
• Array.union: sugarjs