Generator Extensions

Like Reactive Extensions for Generators

Installation

Add the library to your project

npm install --save generator-extensions

Activate the extensions

require('generator-extensions')

Use the synchronous extensions

function* range(a, b) {
    for (let i = a; i < b; i++) {
        yield i
    }
}

const zero = range(10,20)
    .flatMap(x => [x, -x])
    .map(x => x * 2)
    .reduce((a, b) => a + b)

Use the asynchronous extensions

async function* range(a, b) {
    for (let i = a; i < b; i++) {
        yield i
    }
}

const zero = range(10,20)
    .flatMap(x => [x, -x])
    .map(x => x * 2)
    .reduce((a, b) => a + b)

Operators

toArray

Collects the generator into a single array.

➊──➋──➌
.toArray()
[➊, ➋, ➌]

flatMap

The flatMap() method first maps each element using a mapping function, then flattens the result into a new generator.

➊────➋────➌
.flatMap(x => [x, x + 10])
➊─⓫─➋─⓬─➌─⓭

flat

The flat([depth = 1]) flattens each element to a specified depth into a new generator.

[➊, ➋, ➌]────[➊, ➋, ➌]
.flat()
➊─➋─➌─➊─➋─➌

map

The map() method creates a new generator with the results of calling a provided function on every element in the calling generator.

➊────➋────➌
.map(x => x * 2)
➋────➍────➏

entries

The entries() method returns a new generator that contains the key/value pairs for each index in the generator.

➊────➋────➌
.entries()
[0,➊]──[1,➋]──[2,➌]

filter

The filter() method creates a new generator with all elements that pass the test implemented by the provided function.

➊────➋────➌
.filter(x => x < 2)
➊────➋

find

The find() method returns the value of the first element in the provided generator that satisfies the provided testing function.

➊────➋────➌
.find(x => x > 1)
➋

findIndex

The findIndex() method returns the index of the first element in the generator that satisfies the provided testing function. Otherwise, it returns -1, indicating that no element passed the test.

➊────➋────➌
.findIndex(x => === 2)
1

keys

The keys() method returns a new generator that contains the keys for each index in the generator.

➊────➋────➌
.keys()
0────1────2

reduce

The reduce() method executes a reducer function (that you provide) on each element of the generator, resulting in a single output value.

➊────➋────➌
.reduce((a, b) => a + b, 0)
6

some

The some() method tests whether at least one element in the generator passes the test implemented by the provided function. It returns a Boolean value.

➊────➋────➌
.some(x => x > 2)
true

every

The every() method tests whether all elements in the generator pass the test implemented by the provided function. It returns a Boolean value.

➊────➋────➌
.every(x => x > 2)
false

tap

Execute a function for each element without changing the value emitted.

➊────➋────➌
.tap(x => console.log(x))
➊────➋────➌

count

Counts the number of elements and returns it as a number. ➊────➋────➌
.count()
3

forEach

The forEach() method executes a provided function once for each generator element.

parallel (async only)

The parallel() method executes a provided async function in parallel with other elements, up to a limit provided by the second parameter (default: Infinity). The resulting generator may be in a different order than the source generator.

➊─➋─➌─➍─➎─➏─➐─➑─➒
.parallel(async x => x, 3)
➊───➍───➐
───➋───➎───➑
──────➌───➏───➒
...
➊─➋─➍─➌─➎─➐─➏─➑─➒