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

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

As mentioned above, this method uses the same algorithm as Array.prototype.reduce(). And thus the same polyfill can be used here: simply replace Array.prototype.reduce with TypedArray.prototype.reduce.

Specifications

Browser compatibility

See also

• TypedArray.prototype.reduceRight()
• Array.prototype.reduce()