TypedArray.prototype.reduce()

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

reduce(callbackFn)
reduce(callbackFn, initialValue)

Parameters

callbackFn

A function to execute for each element in the typed array. Its return value becomes the value of the accumulator parameter on the next invocation of callbackFn. For the last invocation, the return value becomes the return value of reduce(). The function is called with the following arguments:

accumulator

The value resulting from the previous call to callbackFn. On first call, initialValue if specified, otherwise the value of array[0].

currentValue

The value of the current element. On first call, the value of array[0] if an initialValue was specified, otherwise the value of array[1].

currentIndex

The index position of currentValue in the typed array. On first call, 0 if initialValue was specified, otherwise 1.

array

The typed array reduce() was called upon.

initialValue Optional

A value to which accumulator is initialized the first time the callback is called. If initialValue is specified, callbackFn starts executing with the first value in the typed array as currentValue. If initialValue is not specified, accumulator is initialized to the first value in the typed array, and callbackFn starts executing with the second value in the typed array as currentValue. In this case, if the typed array is empty (so that there's no first value to return as accumulator), an error is thrown.

Return value

The value that results from the reduction.

Description

The reduce method executes the callbackFn 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 callbackFn 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, accumulator and currentValue can be one of two values. If initialValue is provided in the call to reduce, then accumulator will be equal to initialValue and currentValue will be equal to the first value in the typed array. If no initialValue was provided, then accumulator 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 callbackFn.

Examples

Sum up all values within an array

const total = new Uint8Array([0, 1, 2, 3]).reduce((a, b) => a + b);
// total === 6

Specifications

Specification
ECMAScript Language Specification
# sec-%typedarray%.prototype.reduce

Browser compatibility

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See also