node-core-library.async.mapasync_1.md

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Home > @rushstack/node-core-library > Async > mapAsync

Async.mapAsync() method

Given an input array and a callback function, invoke the callback to start a promise for each element in the array. Returns an array containing the results.

Signature:

static mapAsync<TEntry extends IWeighted, TRetVal>(iterable: Iterable<TEntry> | AsyncIterable<TEntry>, callback: (entry: TEntry, arrayIndex: number) => Promise<TRetVal>, options: IAsyncParallelismOptions & {
        weighted: true;
    }): Promise<TRetVal[]>;

Parameters

Parameter	Type	Description
iterable	Iterable<TEntry> | AsyncIterable<TEntry>	the array of inputs for the callback function
callback	(entry: TEntry, arrayIndex: number) => Promise<TRetVal>	a function that starts an asynchronous promise for an element from the array
options	IAsyncParallelismOptions & { weighted: true; }	options for customizing the control flow

Returns:

Promise<TRetVal[]>

an array containing the result for each callback, in the same order as the original input array

Remarks

This API is similar to the system Array#map<></>, except that the loop is asynchronous, and the maximum number of concurrent units can be throttled using IAsyncParallelismOptions.concurrency<></>. Using the IAsyncParallelismOptions.weighted option, the weight of each operation can be specified, which determines how many concurrent units it takes up.

If callback throws a synchronous exception, or if it returns a promise that rejects, then the loop stops immediately. Any remaining array items will be skipped, and overall operation will reject with the first error that was encountered.