A generator call creates an iterator instead of immediately running the generator body. The iterator lets you request values one at a time, either with next() or through a for...of loop. section 6.2
Each next() call runs the generator until its next yield, then returns an object containing the yielded value and a done flag. The generator suspends until another request; when it finishes, done is true and value is undefined. section 6.2.1
Iterators make generator-produced sequences useful for:
- Requesting successive values, such as IDs from a generator with an ongoing loop. section 6.2.2
- Traversing DOM nodes with a generator and for...of, as an alternative to recursive traversal. section 6.2.2
Listing 6.2. Controlling a generator through an iterator object
function* WeaponGenerator(){ #A
yield "Katana"; #A
yield "Wakizashi"; #A
}
const weaponsIterator = WeaponGenerator(); #B
const result1 = weaponsIterator.next(); #C
assert(typeof result1 === "object" #D
&& result1.value === "Katana" #D
&& !result1.done, #D
"Katana received!"); #D
const result2 = weaponsIterator.next(); #E
assert(typeof result2 === "object" #E
&& result2.value === "Wakizashi" #E
&& !result2.done, #E
"Wakizashi received!"); #E
const result3 = weaponsIterator.next(); #F
assert(typeof result3 === "object" #F
&& result3.value === undefined #F
&& result3.done, #F
"There are no more results!"); #F
Follow the iterator’s successive next() calls and compare each returned value and done flag. section 6.2.1
