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.

Syntax

// Arrow function
reduce((accumulator, currentValue) => { ... } )
reduce((accumulator, currentValue, index) => { ... } )
reduce((accumulator, currentValue, index, array) => { ... } )
reduce((accumulator, currentValue, index, array) => { ... }, initialValue)

// Callback function
reduce(callbackFn)
reduce(callbackFn, initialValue)

// Inline callback function
reduce(function callbackFn(accumulator, currentValue) { ... })
reduce(function callbackFn(accumulator, currentValue, index) { ... })
reduce(function callbackFn(accumulator, currentValue, index, array){ ... })
reduce(function callbackFn(accumulator, currentValue, index, array) { ... }, initialValue)

Parameters

callbackFn

Function to execute on each value in the typed array, taking four arguments:

accumulator: 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 callbackFn.

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

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

Browser compatibility

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