1const _quote_filter = _.map(quote_state, (val, key) => {   if (val) {      return key   }})console.log(_quote_filter) //=> [ 'btc', undefined, undefined ]

1function square(n) {
2  return n * n;
3}
4 
5_.map([4, 8], square);
6// => [16, 64]
7 
8_.map({ 'a': 4, 'b': 8 }, square);
9// => [16, 64] (iteration order is not guaranteed)
10 
11var users = [
12  { 'user': 'barney' },
13  { 'user': 'fred' }
14];
15 
16// The `_.property` iteratee shorthand.
17_.map(users, 'user');
18// => ['barney', 'fred']