leebyron / ecmascript-iterator-hof Goto Github PK

The new for ... of syntax ignores the completion value, so it would make sense to ignore it for the different functions introduced here.

function *example(){
 yield 1;
 yield 2;
 return 3;
}

for(let i of example()) console.log(i);

Outputs

1
2

On can achieve the exact same effect by chaining map and flatten. When xstream (an Observable implementation) was being made, the creator, @staltz, omitted "flatMap" because [it was easier to understand]. I think this reasoning applies to higher order functions with Iterators.

Consider this snippet in the readme which incorrectly suggests the return value of flatten is an array.

var deepValues = [ [ 'A' ], [[ 'B' ]], 'C' ]
var flat = deepValues.values().flatten() // [ 'A', ['B'], 'C' ]

Adding the method collect:

class Iterator<T> {
    collect<R>(fn: (iterator: Iterator<T>) => R): R;
}

Would allow:

var deepValues = [ [ 'A' ], [[ 'B' ]], 'C' ]
var flat = deepValues.values().flatten().collect(Array.from) // [ 'A', ['B'], 'C' ]

Once you introduce a series of operators, people are bound to want to have more.
I think it would be a good idea to introduce a .bind(fn, ...args) operator which would allow chaining with custom operators without having to subclass or modify the prototype.

There were several discussions about something like that from pre-es6 strawmans, but it's still missed in https://github.com/tc39/proposals

It's not immediately clear to me whether this is the case.

Add Iterator[@@species] accessor property and IteratorSpeciesCreate abstract operation so that:

class MyIterator extends Iterator {}
new MyIterator().map(x => x) instanceof MyIterator // true

See:

1. get Array [ @@species ]
2. ArraySpeciesCreate

Would it make sense for this proposal to also define the same functions for Async Iterables to kill two birds with one stone?

Having higher order functions on async iterables would make async programming extremely powerful.

Is this an opportunity to spec the functions as generators? A few examples:

class Iterator {
    *concat(...iterators) {
        yield* this;
        for (iterator in iterators) {
            yield* iterator;
        }
    }

    *map(mapFn) {
        for (value in this) {
            yield mapFn(value);
        }
    }

    *filter(filterFn) {
        for (value in this) {
            if (filterFn(value)) {
                yield value;
            }
        }
    }

    *flatten() {
        for (iterator in this) {
            yield* iterator;
        }
    }
}