reduce

The reduce() function reduces a generator to a single value by applying an accumulator function to each element. It also allows early exit with exit().

Interactive example

Syntax

Classic signature

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

Curried signature

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

Parameters

• iterator: The generator to reduce
• startValue: Initial accumulator value (use DGenerator.reduceFrom() for objects)
• theFunction: 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

The final accumulated value.

See also

• asyncReduce - Asynchronous version of reduce
• map - Transforms the elements of a generator
• filter - Filters the elements of a generator

Sources

• MDN Web Docs - Array.prototype.reduce()