TypedArray.prototype.reduce()

The reduce() method of TypedArray instances executes a user-supplied "reducer" callback function on each element of the typed array, in order, passing in the return value from the calculation on the preceding element. The final result of running the reducer across all elements of the typed array is a single value. This method has the same algorithm as Array.prototype.reduce().

Try it

const uint8 = new Uint8Array([0, 1, 2, 3]);

function sum(accumulator, currentValue) {
  return accumulator + currentValue;
}

console.log(uint8.reduce(sum));
// Expected output: 6

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 the first call, its value is initialValue if the latter is specified; otherwise its value is array[0].

currentValue

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

currentIndex

The index position of currentValue in the typed array. On the first call, its value is 0 if initialValue is 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 running the "reducer" callback function to completion over the entire typed array.

Exceptions

TypeError

Thrown if the typed array contains no elements and initialValue is not provided.

Description

See Array.prototype.reduce() for more details. This method is not generic and can only be called on typed array instances.

Examples

Sum up all values within an array

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

Specifications

Browser compatibility

See also

• Polyfill of TypedArray.prototype.reduce in core-js
• JavaScript typed arrays guide
• TypedArray
• TypedArray.prototype.map()
• TypedArray.prototype.reduceRight()
• Array.prototype.reduce()
• Object.groupBy()
• Map.groupBy()