The some() method of Iterator instances is similar to Array.prototype.some: it tests whether at least one element in the array passes the test implemented by the provided function. It returns a boolean value.
Syntax
some(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 the callback function returns a
value for at least one element. Otherwise, false.
Description
some() iterates the iterator and invokes the callbackFn function once for each element. It returns true immediately if the callback function returns a truthy value. Otherwise, it iterates until the end of the iterator and returns false. If some() returns true, 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, some() returns true as soon as the first truthy value is found. If the callbackFn always returns a falsy value, the method never returns.
Examples
Using some()
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().some(isEven)); // true
const isNegative = (x) => x < 0;
const isPositive = (x) => x > 0;
console.log(fibonacci().take(10).some(isPositive)); // false
console.log(fibonacci().some(isNegative)); // Never completes
Calling some() 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.some(isEven)); // true
console.log(seq.next()); // { value: undefined, done: true }