Lodash is a library of utilities for manipulating and examining objects and arrays.

Implicit chaining with _(arr1) and explicit chaining with _.chain(arr1) work in similar ways. The examples below show how they differ slighlty.

Explicit chaining with _.chain(...)

var arr1 = [10, 15, 20, 25, 30, 15, 25, 35];

var sumOfUniqueValues = _.chain(arr1)
    .uniq()
    .sum()       // sum returns a single value
    .value();    //   which must be unwrapped manually with explicit chaining

// sumOfUniqueValues is now 135

Implicit chaining with _(...)

var arr1 = [10, 15, 20, 25, 30, 15, 25, 35];

var sumOfUniqueValues = _(arr1)
    .uniq()
    .sum();      // sum returns a single value and is automatically unwrapped
                 //   with implicit chaining

// sumOfUniqueValues is now 135

The two behave differently when ending the chain with an operation that returns a single value: With implicit chaining, the "unwrapping" of the single value is implied. (Thus no need to call .value().)

(When the implicit chain ends with a collection value, you'll still need to unwrap the result with .value().)