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.
Syntax
every(callbackFn)
Parameters
callbackFn- : 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:
element- : The current element being processed.
index- : The index of the current element being processed.
- : 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:
Return value
true if callbackFn returns a
value for every element. Otherwise, false.
Description
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.
Examples
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(seq.next()); // { value: undefined, done: true }