I want to do something like as follows

_(data)
  .map(() => /** ... */)
  .reduce(function (modifier, doc) {
    modifier.$set = modifier.$set || {};
    modifier.$set.names = doc.names;
    return modifier;
  }, {})
  .map(() => /** ... */)
  .flatten()

However, it appears that after reduce, the chain breaks.

Is there a way to continue the chain from the value returned by reduce?

I want to do something like as follows

_(data)
  .map(() => /** ... */)
  .reduce(function (modifier, doc) {
    modifier.$set = modifier.$set || {};
    modifier.$set.names = doc.names;
    return modifier;
  }, {})
  .map(() => /** ... */)
  .flatten()

However, it appears that after reduce, the chain breaks.

Is there a way to continue the chain from the value returned by reduce?

• javascript
• underscore.js
• lodash

• so what does the reduce return? No way for us to reproduce your issue. A demo that replicates it would help – charlietfl Commented Oct 8, 2015 at 19:40
• something that looks like { $set: { names: [ 'alex', 'jeff' ] } } – corvid Commented Oct 8, 2015 at 19:42
• yeah, that's just an example though. I mean I want to continue with the chain as this object – corvid Commented Oct 8, 2015 at 19:43
• start a new chain, reduce returns it own non-array thing, which can't be chained... – dandavis Commented Oct 8, 2015 at 19:45

2 Answers 2

reduce() method is not guaranteed to produce a collection (array, object, or string) upon which other methods could operate, therefore it makes no sense that it could be chainable by default.

From lodash documentation on lodash object (_):

Methods that operate on and return arrays, collections, and functions can be chained together. Methods that retrieve a single value or may return a primitive value will automatically end the chain returning the unwrapped value.

_ documentation

You can however explicitly enforce chaining by using _.chain(). This would allow for single values and primitives to be explicitly returned within lodash wrapper for continued chaining.

So for your code that might look like:

_.chain(data)
  .map(() => /** ... */)
  .reduce(function (modifier, doc) {
    modifier.$set = modifier.$set || {};
    modifier.$set.names = doc.names;
    return modifier;
  }, {})
  .map(() => /** ... */)
  .flatten()

_.chain() documentation

The lodash docs say that reduce() is not chainable. See here: "The wrapper methods that are not chainable by default are: ... reduce" https://lodash./docs#_