generator_helpers

This module monkey patches proposal-iterator-helpers onto JavaScript or TypeScript generators. After importing this module, methods that can normally only be used on arrays can also be used on generators. Methods that take a function as an argument are given the value and index of elements as parameters. A list of all monkey patched methods is provided below. Check the proposal-iterator-helpers repository for more information and examples.

• .map(mapperFn)
• .filter(filtererFn)
• .take(limit)
• .drop(limit)
• .asIndexedPairs()
• .flatMap(mapperFn)
• .reduce(reducer [, initialValue ])
• .toArray()
• .forEach(fn)
• .some(fn)
• .every(fn)
• .find(fn)

Additionally range is provided as a helper generator as well as the Iterator.from method.

• range(stop)
• range(start, stop [, step = 1 ])
• .from(object)

Examples

.map(mapperFn) and .toArray()

The .map(mapperFn) method yields the results of mapperFn called with the value and index of every element passed as parameters.

The .toArray() method returns the generator cast to an Array.

import "https://deno.land/x/generator_helpers/monkey_patch.ts";
import { assertEquals } from "https://deno.land/std/testing/asserts.ts";

function* lowercase(): Generator<string> {
  yield "a";
  yield "b";
  yield "c";
}

const uppercase = lowercase()
  .map((char) => char.toUpperCase())
  .toArray()
  .join("");

assertEquals(uppercase, "ABC");

range(limit) and .reduce(reducer [, initialValue ])

The range(stop) or range(start, stop [, step = 1 ]) function is not included in iterator-helpers proposal, but is included as a utility. It yields from 0 up to, but not included, the y0 parameter. If y1 and yd are provided it yields from y0 until y1 with steps of yd. The yd parameter is 1 by default.

The .reduce(reducer [, initialValue ]) method applies the reducer function to each value using the previous result for for the first parameter. The first time it is called initialValue is used if provided or else the first item of the generator. The third parameter that is provided to mapperFn is the current index.

import { range } from "https://deno.land/x/generator_helpers/monkey_patch.ts";
import { assertEquals } from "https://deno.land/std/testing/asserts.ts";

const sum = range(10).reduce((prev, cur) => prev + cur, 0);

assertEquals(sum, 45);

.flatMap(mapperFn)

The .flatMap(mapperFn) method the results from calls to mapperFn. Thereby flattening the generator one level.

import { range } from "https://deno.land/x/generator_helpers/monkey_patch.ts";
import { assertEquals } from "https://deno.land/std/testing/asserts.ts";

const oneArray = range(5).flatMap((value) => Array(value).fill(value));

assertEquals(oneArray, [1, 2, 2, 3, 3, 3, 4, 4, 4, 4]);