A simple iterable without items inside, implementing the right protocol
the iteratorFunction needs to comply to the iterator protocol
must return an object
function iteratorFunction() {}
assert.equal(typeof iteratorFunction(), 'object');
the object must have a function assigned to a key next
function iteratorFunction() { return {next: () => ({done: true})}; }
assert.equal(typeof iteratorFunction().next, 'function');
calling next() must return an object with {done: true}
function iteratorFunction() { return {next: () => ({done: true})}; }
assert.deepEqual(iteratorFunction().next(), {done: true});
the iterable
must be an object
function iteratorFunction() { return {next: () => ({done: true})}; }
const iterable = {[Symbol.iterator]: iteratorFunction};
assert.equal(typeof iterable, 'object');
must have the iterator function assigned to the key Symbol.iterator
function iteratorFunction() { return {next: () => ({done: true})}; }
const iterable = {[Symbol.iterator]: iteratorFunction};
assert.equal(iterable[Symbol.iterator], iteratorFunction);
using the iterable
it contains no values
function iteratorFunction() { return {next: () => ({done: true})}; }
const iterable = {[Symbol.iterator]: iteratorFunction};
let values;
for (let value of iterable) {
values += value;
}
assert.equal(values, '');
has no .length property
function iteratorFunction() { return {next: () => ({done: true})}; }
const iterable = {[Symbol.iterator]: iteratorFunction};
const hasLengthProperty = iterable;
assert.equal(hasLengthProperty, false);
can be converted to an array
using Array.from()
function iteratorFunction() { return {next: () => ({done: true})}; }
const iterable = {[Symbol.iterator]: iteratorFunction};
const arr = iterable;
assert.equal(Array.isArray(arr), true);
where .length is still 0
function iteratorFunction() { return {next: () => ({done: true})}; }
const iterable = {[Symbol.iterator]: iteratorFunction};
const arr = iterable;
const length = arr.length;
assert.equal(length, 0);