Name
Array.reduce() — compute a value from the elements of an array
Availability
ECMAScript 5
Synopsis
array
.
reduce
(
f
)
array
.
reduce
(
f
,
initial
)
Arguments
f
A function that combines two values (such as two array elements) and returns a new “reduced” value.
initial
An optional initial value to seed the array reduction with. If this argument is specified,
reduce()
behaves as if it had been inserted at the start ofarray
.
Returns
The reduced value of the array, which is the return value of
the last invocation of f
.
Description
The reduce()
method expects
a function f
as its first argument. This
function should behave like a binary operator: it takes two values,
performs some operation on them and returns a result. If
array
has n
elements, the reduce()
method invokes
f
n-1
times to reduce those elements to a single combined value. (You may
be familiar with this array reduction operation from other
programming languages where it is sometimes called “fold” or
“inject”.)
The first invocation of f
is passed
the first two elements of array
. Each
subsequent invocation of f
is passed the
return value of the previous invocation and the next element (in
ascending order) of array
. The return
value of the final invocation of f
becomes the return value of the reduce()
method itself.
reduce()
may be invoked
with an optional second argument,
initial
. If
initial
is specified, then reduce()
behaves as if that argument has
been inserted at the beginning of array
(it does not actually modify array
, however). Another ...
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