asyncReduce

The asyncReduce() function reduces a generator to a single value by applying an asynchronous accumulator function to each element. Asynchronous version of reduce().

Interactive example

Syntax

Classic signature

function asyncReduce<
	GenericElement extends unknown,
	GenericReduceFrom extends GeneratorEligibleReduceFromValue,
>(
	iterator: Iterable<GenericElement> | AsyncIterable<GenericElement>,
	startValue: GenericReduceFrom,
	theFunction: (
		params: GeneratorReduceFunctionParams<
			GenericElement,
			GeneratorReduceFromValue<GenericReduceFrom>
		>
	) => GeneratorReduceExitOrNext<GeneratorReduceFromValue<GenericReduceFrom>>
): Promise<GeneratorReduceFromValue<GenericReduceFrom>>

Curried signature

function asyncReduce<
	GenericElement extends unknown,
	GenericReduceFrom extends GeneratorEligibleReduceFromValue,
>(
	startValue: GenericReduceFrom,
	theFunction: (
		params: GeneratorReduceFunctionParams<
			GenericElement,
			GeneratorReduceFromValue<GenericReduceFrom>
		>
	) => GeneratorReduceExitOrNext<GeneratorReduceFromValue<GenericReduceFrom>>
): (
	iterator: Iterable<GenericElement> | AsyncIterable<GenericElement>
) => Promise<GeneratorReduceFromValue<GenericReduceFrom>>

Parameters

• iterator: The generator (synchronous or asynchronous) to reduce
• startValue: Initial accumulator value (use DGenerator.reduceFrom() for objects)
• theFunction: Asynchronous reduction function that receives:
  • element: The current element
  • index: The element index
  • lastValue: The previous accumulated value
  • next(value): Continues with a new accumulated value
  • exit(value): Ends and returns the value
  • nextWithObject(obj1, obj2): Merges two objects (available if lastValue is an object)

Return value

A Promise that resolves with the final accumulated value.

See also

• reduce - Synchronous version of asyncReduce
• asyncMap - Transforms with an async function
• asyncFilter - Filters with an async function

Sources

• MDN Web Docs - Async iterators