Nice article! It’s true that `_.chain` implementation isn’t really the optimal solutions for chaining usage; and you have well explained some raisons for this. That said, with underscore-es there is the method `_.use` that can be also used to overcome this statut.

import _use from 'underscore-es/use';
import _initial from 'underscore-es/initial';
import _filter from 'underscore-es/filter';
import _union from 'underscore-es/union';
import _last from 'underscore-es/last';

function note (num) {return 'result: '+ (num + 10) + " / 20"}
var test = _use([1, 2, 3, 6, 9])
         .do(_union, [1, 3, 11], [2, 6, 10, 14])
         .do(_filter, (num) => num % 2 == 0)
         .do(_initial)
         .do(_last)
         .do(note)
         .value();
console.log( test );
// => result: 20 / 20