Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The every() method of Iterator instances is similar to Array.prototype.every(): it tests whether all elements produced by the iterator pass the test implemented by the provided function. It returns a boolean value.





A 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:


The current element being processed.


The index of the current element being processed.

Return value

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 their ability to work 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.


Using every()

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 completes

Calling every() always closes the underlying iterator, even if the method early-returns. The iterator is never left in a half-way state.

const seq = fibonacci();
console.log(seq.every(isEven)); // false
console.log(; // { value: undefined, done: true }


Iterator Helpers
# sec-iteratorprototype.every

Browser compatibility

BCD tables only load in the browser

See also