2-array-some

Imagine you have an array of numbers:

var numbers = [1, 3, -1, 5, 9];

You know that the array is supposed to contain positive numbers, but you want to check if it also contains any negative numbers.

We can write a function that checks this:

function isNegative(number) {
  return number < 0;
}

To check your array of numbers, you'd have to run this function against every number in the array. Thankfully there is an array method that does just this!

.some()

Searches through an array and returns true if at least one array item satisifies the predicate function you provided.

var containsNegative = ages.some(isNegative);

console.log(containsNegative); // logs true