--- /dev/null
+'use strict';
+var $ = require('../internals/export');
+var IS_PURE = require('../internals/is-pure');
+var anObject = require('../internals/an-object');
+var aFunction = require('../internals/a-function');
+var getSetIterator = require('../internals/get-set-iterator');
+var iterate = require('../internals/iterate');
+
+// `Set.prototype.reduce` method
+// https://github.com/tc39/proposal-collection-methods
+$({ target: 'Set', proto: true, real: true, forced: IS_PURE }, {
+ reduce: function reduce(callbackfn /* , initialValue */) {
+ var set = anObject(this);
+ var iterator = getSetIterator(set);
+ var noInitial = arguments.length < 2;
+ var accumulator = noInitial ? undefined : arguments[1];
+ aFunction(callbackfn);
+ iterate(iterator, function (value) {
+ if (noInitial) {
+ noInitial = false;
+ accumulator = value;
+ } else {
+ accumulator = callbackfn(accumulator, value, value, set);
+ }
+ }, undefined, false, true);
+ if (noInitial) throw TypeError('Reduce of empty set with no initial value');
+ return accumulator;
+ }
+});