Underscore.js: how to chain custom functions

Question

Using Underscore.js, I can write the following which returns 42:

_([42, 43]).chain()
    .first()
    .value()

I have custom f

Answer 1

Many ways to easily achieve this, here is one such solution:

  _.chain([42,43])
    .first(1)
    .map(double)
    .first()
    .value();
    // 84

However, I would recommend using Ramda then with auto-curry and pipe / compose these kinds of tasks are trivial:

R.pipe(R.head, R.multiply(2))([42, 43]);  // 84

equivalent to:

R.compose(R.multiply(2), R.head)([42, 43]);  // 84

If you wanted to extend the solution to take say the first 2 items, instead of a single value, as requested by the OP, then:

R.pipe(R.take(2), R.map(R.multiply(2)))([42, 43])  // [84, 86]

However, in Ramda R.compose is preferred. Either way, for trivial tasks like this, it does tend to be more convenient and easy to use.