Chaining
Remarks#
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 135Implicit 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 135The 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().)
Chaining
Any lodash collection method has two syntaxes.
Without chaining:
var arr1 = [10, 15, 20, 25, 30, 15, 25, 35];
var arr2 = _.filter(arr1, function(item){ return item % 10 === 5 });
// arr2 now contains [15, 25, 15, 25, 35]
var arr3 = _.uniq(arr2);
// arr3 now contains [15, 25, 35]
var arr4 = _.map(arr3, function(item){ return item + 1 });
// arr4 now contains [16, 26, 36]With chaining:
var arr1 = [10, 15, 20, 25, 30, 15, 25, 35];
var arr4 = _(arr1)
.filter(function(item){ return item % 10 === 5 })
.uniq()
.map(function(item){ return item + 1 })
.value();
// arr4 now contains [16, 26, 36] without creating the intermediate results.The chaining version of this is actually more efficient, since no intermediate results are created. The expressions are evaluated lazily by the call to .values() at the end of the chain.