The reduceRight() method applies a function against an accumulator and each value of the typed array (from right-to-left) has to reduce it to a single value. This method has the same algorithm as Array.prototype.reduceRight(). TypedArray is one of the typed array types here.

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reduceRight(callbackFn, initialValue)



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 reduceRight(). The function is called with the following arguments:


The value previously returned in the last invocation of the callback, or initialValue, if supplied. (See below.)


The current element being processed in the typed array.


The index of the current element being processed in the typed array.


The typed array reduceRight() was called upon.

initialValue Optional

Value to use as accumulator to the first call of the callbackFn. If no initial value is supplied, the last element in the array will be used and skipped. Calling reduceRight() on an empty array without an initial value creates a TypeError.

Return value

The value that results from the reduction.


The reduceRight 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 call to the reduceRight callback would look something like this:

typedarray.reduceRight((accumulator, currentValue, index, typedarray) => {
  // ...

The first time the function is called, the accumulator and currentValue can be one of two values. If an initialValue was provided in the call to reduceRight, then accumulator will be equal to initialValue and currentValue will be equal to the last value in the typed array. If no initialValue was provided, then accumulator will be equal to the last value in the typed array and currentValue will be equal to the second-to-last value.

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.


Sum up all values within an array

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


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

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See also