An extensions for objects with Iteration Protocol for JS
Platform | Build Status |
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Linux | |
Windows |
ES2015 introduces a new feature, namely the Iterations Protocol. The protocol consists of 2 protocols:
-
The iterable protocol allows JavaScript objects to define or customize their iteration behavior, such as what values are looped over in a for..of construct. Some built-in types are built-in iterables with a default iteration behavior, such as Array or Map, while other types (such as Object) are not.
In order to be iterable, an object must implement the @@iterator method, meaning that the object (or one of the objects up its prototype chain) must have a property with a @@iterator key which is available via constant Symbol.iterator:
[Symbol.iterator]
- A zero arguments function that returns an object, conforming to the iterator protocol.
Whenever an object needs to be iterated (such as at the beginning of a for..of loop), its @@iterator method is called with no arguments, and the returned iterator is used to obtain the values to be iterated.
-
The iterator protocol defines a standard way to produce a sequence of values (either finite or infinite), and potentially a return value when all values have been generated.
An object is an iterator when it implements a next() method with the following semantics:
- next
- A zero arguments function that returns an object with at least the following two properties:
done
(boolean)- Has the value
true
if the iterator is past the end of the iterated sequence. In this casevalue
optionally specifies the return value of the iterator. - Has the value
false
if the iterator was able to produce the next value in the sequence. This is equivalent of not specifying the done property altogether.
- Has the value
value
- any JavaScript value returned by the iterator.
- Can be omitted when
done
istrue
.
- The next method always has to return an object with appropriate properties including
done
andvalue
. - If a non-object value gets returned (such as
false
orundefined
), a TypeError ("iterator.next() returned a non-object value") will be thrown.
- A zero arguments function that returns an object with at least the following two properties:
- next
Iterable intends to unify all iterable objects, be it a built-in iterable (e.g. Array, String, Map) or a user-made iterable (e.g. user-defined generators, objects with Symbol.iterator property), acting as the de-facto superset.
By taking advantage of the Iteration Protocol, Iterable can provide operators that allows to transform any iterable objects.
Iterable operators are not strict to Iterable instance, they expect the first parameters to be an iterable object, regardless of the implementation. For example,
Iterable.concat('Hello', [1, 2, 3, 4, 5]);
creates an iterable that yields the characters of 'Hello' and the values of [1, 2, 3, 4, 5]
sequentially.
First, I would like to point out that at the time I have written almost half of the library, I stumbled upon the library IxJS while looking for Rx libraries, and to my surprise, it has the same goal as my library's.
So, what are the differences?
Iterable doesn't/isn't:
- support async.
- expose the operators as an individual module.
- written in TypeScript.
- have operators that returns a single value from an aggregation (e.g reduce), instead, they are considered as a singular Iterable (an Iterable with one element).
- handle errors.
Iterable does/is:
- support chaining operators for an Iterable as well as provide these operators as a static member, allowing class deconstruction.
- allow bracket notation for accessing the nth-yield of the Iterable.
- throw runtime errors. If an error occurs, the errors are thrown synchronously on iteration.
- know if an object is iterable by concept or not, allowing non-Iterable instances to have access with the Iterable operators.
Method Counterparts
Iterable | IxJS | Notes |
---|---|---|
all |
every |
Returns a singular Iterable that yields the boolean result. |
any |
some |
Returns a singular Iterable that yields the boolean result. |
average |
average |
Returns a singular Iterable that yields the number result. |
breadthFirst |
||
breakWith |
||
buffer |
buffer |
Doesn't have the skip mechanism. |
cache |
||
compose |
pipe |
|
concat |
concat , of , endWith |
Unlike the IxJS concat , Iterable concat allows to concat non-Iterable values. |
contains |
includes |
Doesn't have the skip mechanism. Returns a singular Iterable that yields the boolean result. |
count |
count |
Returns a singular Iterable that yields the number result. |
defaultIfEmpty |
defaultIfEmpty |
|
depthFirst |
||
diff |
||
distinct |
distinct |
Doesn't have the compare mechanism. Strict equality is used. |
distinctAdjacent |
distinctUntilChanged |
Doesn't have the compare mechanism. Strict equality is used. |
doWhile |
doWhile |
|
elementAt |
elementAt |
Returns a singular Iterable that yields the result. |
empty |
empty |
|
equal |
sequenceEqual |
Returns a singular Iterable that yields the boolean result. |
filter |
filter |
|
find |
find |
Instead of yielding the passing value, ```find`` yields the index. Returns a singular Iterable that yields the number result. |
first |
first |
Returns a singular Iterable that yields the result. |
flat |
flatten |
Iterable flat only flattens a single layer. To flatten all layers, use depthFirst |
flatMap |
flatMap |
|
ignoreElements |
ignoreElements |
|
indexOf |
||
innerJoin |
innerJoin |
|
intercalate |
||
intersect |
intersect |
|
intersperse |
||
isEmpty |
isEmpty |
Returns a singular Iterable that yields the boolean result. |
just |
||
last |
last |
|
leftJoin |
||
map |
map |
|
max |
max |
Returns a singular Iterable that yields the result. |
min |
min |
Returns a singular Iterable that yields the result. |
onDone |
||
onStart |
||
onYield |
||
outerJoin |
||
partition |
partition |
|
range |
range |
Unlike IxJS, Iterable range allows negative slope, and custom step size. |
reduce |
reduce |
Returns a singular Iterable that yields the result. |
reduceRight |
reduceRight |
Returns a singular Iterable that yields the result. |
repeat |
repeat |
|
replace |
||
reverse |
reverse |
|
scan |
scan |
|
scanRight |
scanRight |
|
skip |
skip |
|
skipLast |
skipLast |
|
skipUntil |
||
skipWhile |
skipWhile |
|
sort |
orderBy |
|
sorted |
Returns a singular Iterable that yields the boolean result. | |
spanWith |
||
split |
||
startWith |
startWith |
|
step |
||
sum |
sum |
Returns a singular Iterable that yields the result. |
take |
take |
|
takeLast |
takeLast |
|
takeUntil |
||
takeWhile |
takeWhile |
|
toArray |
toArray |
|
whileDo |
while |
|
zip |
zip |
|
case |
||
catch |
Iterable throws the error synchronously. | |
catchWith |
Iterable throws the error synchronously. | |
chain |
||
concatAll |
||
defer |
Meh | |
expand |
||
find |
||
for |
||
generate |
Iterable supports Generators. | |
groupBy |
||
groupJoin |
||
if |
||
memoize |
||
ofEntries |
Use Object.entries instead. |
|
ofKeys |
Use Object.keys instead. |
|
ofValues |
Use Object.values instead. |
|
onErrorResumeNext |
Iterable doesn't support fallbacks. | |
pairwise |
||
pluck |
||
publish |
||
retry |
Iterable doesn't support fallbacks. | |
share |
||
single |
Isn't encouraged. | |
tap |
use the doXXXX operators. |
|
union |
NPM
npm install @lxsmnsyc/iterable-js
CDN
- jsDelivr
<script src="https://cdn.jsdelivr.net/npm/@lxsmnsyc/iterable-js/dist/index.min.js"></script>
- unpkg
<script src="https://unpkg.com/@lxsmnsyc/iterable-js/dist/index.min.js"></script>
const Iterable = require('iterable-js');
Loading the CommonJS module provides the Iterable class.
Loading the JavaScript file for the iterable-js provides the Iterable class.
Creates a partition of iterables in which the first iterable yields the even numbers, while the second iterable yields the odd numbers.
const evenOdd = Iterable.range(1, 200).partition(x => x % 2 === 0);
for (const i of evenOdd[0].map(x => `Next Even: ${x}`)) {
console.log(i);
}
for (const i of evenOdd[1].map(x => `Next Odd: ${x}`)) {
console.log(i);
}
All operators of Iterable are both static and non-static (except for a few ones), allowing chainable and direct transformations.
Both examples below does the same thing.
for (const i of Iterable.filter('Hello World', x => x === x.toUpperCase())) {
console.log(i);
}
for (const i of new Iterable('Hello World').filter(x => x === x.toUpperCase())) {
console.log(i);
}
Iterable treats generator functions as an iterable object, even if it doesn't implement the iterable protocol.
const iterable = new Iterable(function* () {
yield 1;
yield 2;
yield 3;
});
for (const i of iterable) {
console.log(i);
}
To create your own operator, you must pass functions to the compose
method. The functions provided must receive a single parameter, which refers to the chained Iterable, and must return an Iterable.
const getOdds = source => source.filter(x => x % 2 === 1);
for (const i of Iterable.range(1, 1000).compose(getOdds)) {
console.log(i);
}
compose
can accept multiple functions, allowing to build pipelines of operators.
Clone the repo then run
npm install
To build distributables, coverages and tests:
npm run build