The every() method of Iterator instances is similar to Array.prototype.every(): it returns false if it finds an element that does not satisfy the provided testing function. Otherwise, if the iterator is exhausted without finding such an element, it returns true.
every(callbackFn)callbackFnA function to execute for each element produced by the iterator. It should return a truthy value to indicate the element passes the test, and a falsy value otherwise. The function is called with the following arguments:
true if callbackFn returns a truthy value for every element. Otherwise, false.
every() iterates the iterator and invokes the callbackFn function once for each element. It returns false immediately if the callback function returns a falsy value. Otherwise, it iterates until the end of the iterator and returns true. If every() returns false, the underlying iterator is closed by calling its return() method.
The main advantage of iterator helpers over array methods is that they are lazy, meaning that they only produce the next value when requested. This avoids unnecessary computation and also allows them to be used with infinite iterators. With infinite iterators, every() returns false as soon as the first falsy value is found. If the callbackFn always returns a truthy value, the method never returns.
Calling every() always closes the underlying iterator, even if the method early-returns. The iterator is never left in a half-way state.
function* fibonacci() {
let current = 1;
let next = 1;
while (true) {
yield current;
[current, next] = [next, current + next];
}
}
const isEven = (x) => x % 2 === 0;
console.log(fibonacci().every(isEven)); // false
const isPositive = (x) => x > 0;
console.log(fibonacci().take(10).every(isPositive)); // true
console.log(fibonacci().every(isPositive)); // Never completesThe method closes the iterator after returning.
const seq = fibonacci();
console.log(seq.every(isEven)); // false
console.log(seq.next()); // { value: undefined, done: true }