--- /dev/null
+'use strict';
+var anObject = require('../internals/an-object');
+
+// `Map.prototype.emplace` method
+// https://github.com/thumbsupep/proposal-upsert
+module.exports = function emplace(key, handler) {
+ var map = anObject(this);
+ var value = (map.has(key) && 'update' in handler)
+ ? handler.update(map.get(key), key, map)
+ : handler.insert(key, map);
+ map.set(key, value);
+ return value;
+};