core-js/internals/iterator-map.js

'use strict';
var call = require('../internals/function-call');
var aCallable = require('../internals/a-callable');
var anObject = require('../internals/an-object');
var getIteratorDirect = require('../internals/get-iterator-direct');
var createIteratorProxy = require('../internals/iterator-create-proxy');
var callWithSafeIterationClosing = require('../internals/call-with-safe-iteration-closing');

var IteratorProxy = createIteratorProxy(function () {
  var iterator = this.iterator;
  var result = anObject(call(this.next, iterator));
  var done = this.done = !!result.done;
  if (!done) return callWithSafeIterationClosing(iterator, this.mapper, [result.value, this.counter++], true);
});

// `Iterator.prototype.map` method
// https://github.com/tc39/proposal-iterator-helpers
module.exports = function map(mapper) {
  anObject(this);
  aCallable(mapper);
  return new IteratorProxy(getIteratorDirect(this), {
    mapper: mapper
  });
};