The reduce()
method applies a function against an
accumulator and each value of the typed array (from left-to-right) has to reduce it to a
single value. This method has the same algorithm as
Array.prototype.reduce()
. TypedArray is one of the typed
array types here.
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Syntax
typedarray.reduce(callback[, initialValue])
Parameters
callback
- Function to execute on each value in the typed array, taking four arguments:
previousValue
- The value previously returned in the last invocation of the callback, or
initialValue
, if supplied (see below). currentValue
- The current element being processed in the typed array.
index
- The index of the current element being processed in the typed array.
array
- The typed array
reduce()
was called upon.
initialValue
- Optional. Object to use as the first argument to the first call of the
callback
.
Return value
The value that results from the reduction.
Description
The reduce
method executes the callback
function
once for each element present in the typed array, excluding holes in the typed array,
receiving four arguments: the initial value (or value from the previous
callback
call), the value of the current element, the current
index, and the typed array over which iteration is occurring.
The first time the callback is called, previousValue
and
currentValue
can be one of two values. If
initialValue
is provided in the call to reduce
,
then previousValue
will be equal to
initialValue
and currentValue
will be
equal to the first value in the typed array. If no initialValue
was provided, then previousValue
will be equal to the first
value in the typed array and currentValue
will be equal to the
second.
If the typed array is empty and no initialValue
was provided,
TypeError
would be thrown. If the typed array has only one element
(regardless of position) and no initialValue
was provided, or if
initialValue
is provided but the typed array is empty, the solo
value would be returned without calling callback
.
Examples
Sum up all values within an array
var total = new Uint8Array([0, 1, 2, 3]).reduce(function(a, b) {
return a + b;
});
// total == 6
Polyfill
This method uses the same algorithm as Array.prototype.reduce()
, so the
same polyfill can be used here: replace Array.prototype.reduce
with
TypedArray.prototype.reduce
.
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of '%TypedArray%.prototype.reduce' in that specification. |
Browser compatibility
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