Theevery() method ofIterator instances is similar toArray.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 atruthy value to indicate the element passes the test, and afalsy 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.

Return value

true ifcallbackFn returns atruthy value for every element. Otherwise,false.

Description

every() iterates the iterator and invokes thecallbackFn function once for each element. It returnsfalse immediately if the callback function returns a falsy value. Otherwise, it iterates until the end of the iterator and returnstrue. Ifevery() returnsfalse, the underlying iterator is closed by calling itsreturn() 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() returnsfalse as soon as the first falsy value is found. If thecallbackFn 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)); // falseconst isPositive = (x) => x > 0;console.log(fibonacci().take(10).every(isPositive)); // trueconsole.log(fibonacci().every(isPositive)); // Never completes

Callingevery() 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)); // falseconsole.log(seq.next()); // { value: undefined, done: true }

Specifications

Browser compatibility

See also

• Polyfill ofIterator.prototype.every incore-js
• es-shims polyfill ofIterator.prototype.every
• Iterator
• Iterator.prototype.find()
• Iterator.prototype.some()
• Array.prototype.every()