@proc7ts/push-iterator

Push Iteration Protocol

Push iteration protocol is a faster alternative to traditional JavaScript iteration protocol.

It extends Iterator interface with forNext(accept: (this: void, element: T) => void | boolean): boolean method. The latter pushes iterated elements to accept function until there is no more elements, or accept function returns false yo stop iteration. The forNext() method returns true if there are more elements to iterate, or false otherwise. The former is possible only when iteration stopped, i.e. accept returned false.

Rationale

Performance!

Traditional iteration protocol implies a call to next() method and creation of IteratorResult object on each iteration step. The push iteration protocol avoids that.

See benchmarking results for performance comparison.

JavaScript engines optimize native iteration heavily in some situations, especially for arrays. Still, in non-trivial cases the push iteration protocol demonstrates better performance, especially when it deals with push iterators rather with raw ones.

Design Goals

• Performance.

  Push iterators are faster. Still, a lot of the code base relies on raw iterators and arrays. The library contains performance optimizations to deal with it.

• Compatibility.

  • Push iterator implements Iterator interface.
  • Each function in this library handles JavaScript Iterator/Iterable objects in addition to push iterator/push iterable ones.

• Tree shaking support.

  The library API represented by functions. When tree-shaken the unused ones removed from bundles.

API

See the full [API Documentation].

Push Iterable Construction

Each of the following functions returns a push iterable instance:

• overArray(array) - Creates a push iterable over elements of array-like structure.
• overElementsOf(...iterables) - Creates a push iterable over elements of other iterables.
• overEntries(object) - Creates a push iterable over the property key/value entries of the given object.
• overKeys(object) - Creates a push iterable over keys of the given object.
• overMany(...values) - Creates a push iterable over many values.
• overNone() - Returns a push iterable iterator without elements.
• reverseArray(array) - Creates a push iterable over elements of array-like structure in reverse order.

Iterable Consumption

Each of the following functions accepts either Iterable or push iterable:

• itsEach(iterable, action) - Performs the given action for each element of the given iterable.
• itsElements(iterable[, convert]) - Creates a new, shallow-copied array instance containing elements of the source iterable optionally converted by the given converter function. This is an Array.from() function analog optimized for push iterables.
• itsEmpty(iterable): boolean - Checks whether the given iterable is empty.
• itsEvery(iterable, test): boolean - Tests whether all elements of the given iterable pass the test implemented by the provided function.
• itsFirst(iterable): T | undefined - Extracts the first element of the given iterable, if any.
• itsReduction(iterable, reducer, initialValue): T - Applies a function against an accumulator and each element of the given iterable to reduce elements to a single value.
• itsSome(iterable, test): boolean - Tests whether at least one element of the given iterable passes the test implemented by the provided function.

Iterable Transformation

Each of the following functions accepts either Iterable or push iterable, and returns a push iterable:

• filterIt(source, test) - Creates a push iterable with all source iterable elements that pass the test implemented by provided function.
• flatMapIt(source, convert?) - First maps each element of the source iterable using a mapping function, then flattens the result into new push iterable.
• mapIt(source, convert) - Creates a push iterable with the results of calling a provided function on every element of the source iterable.

Array Transformation

Each of the following functions accepts an array-like instance, and returns a push iterable:

• filterArray(aray, test) - Creates a push iterable with all array elements that pass the test implemented by provided function.
• flatMapArray(array, convert?) - First maps each element of the source array using a mapping function, then flattens the result into new push iterable.
• mapArray(array, convert) - Creates a push iterable with the results of calling a provided function on every element of the given array.

Utilities

• iteratorOf(iterable) - Constructs iterator over elements of the given iterable.
• itsIterator(iterable) - Starts iteration over the given iterable. Always returns a push iterator.
• makePushIterator(forNext) - Creates push iterator implementation.