TypedArray.prototype.reduceRight()

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.

Syntax

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

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

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

Examples

Sum up all values within an array

var total = new Uint8Array([0, 1, 2, 3]).reduceRight(function(a, b) {
  return a + b;
});
// total == 6

Specifications

Browser compatibility

See also

• A polyfill of TypedArray.prototype.reduceRight is available in core-js
• TypedArray.prototype.reduce()
• Array.prototype.reduceRight()