This is a utility class to allow lazy iterables in javascript.
You can read here to learn about the problems with the current available iteration methods, but essentially, while normal array methods which consume HOFs are much more readable than a simple for loop, they can be much less performant.
Lazy iterables allow you to gain a significant performance boost in many instances.
const arr = [1, 2, 3, 4, 5];
const arrIter = new LazyIter(arr);
// cube values, remove even results, and then only return elements while the current element is under 30
// takeWhile will skip iterations, unlike filter, making it more performant
arrIter
.map(n => n ** 3)
.filter(n => n % 2 == 1)
.takeWhile(n => n < 30);
// collect is a consumer, which means it no longer returns the iterator
// collect runs through the array and applies all the functions in order
const newArr = arrIter.collect();A lazy iterable first encloses an array (which is never mutated, so no need to clone) and methods are called which are added to an internal array. Nothing happens until a consumer is called, at which point the iterable will internally iterate over the array and return values as a result of calling the functions in order.
A number can alternatively be provided instead of an array, which creates an array of said size, filled with null.
const arrIter = new LazyIter(10);
const reduceFunc = (accum, val) => `${accum} ${val}`;
// reduce is another consumer which works the same as `Array.prototype.reduce`, but it requires a starting value
const str = arrIter.map((_, i) => i).reduce(reduceFunc, '');
console.log(str) // logs: " 0 1 2 3 4 5 6 7 8 9"- The LazyIter instance can alternatively be thrown into the header of a
forloop as it is an iterator.
Consult the tests folder to see methods in use.
docs and explanations can be seen on the wiki as it provided a better format for longer and better-written explanations.
A .entries() method may be added which returns an iterator with the value and index combined in an array, similarly to how Array.prototype.entries works. This is because using the for loop over forEach may be a style preference for many, but the index would have to be retrieved manually, by incrementing a local index variable on each iteration.
This would clean things up, but it is not of vital importance.