Takes an item and returns true if at least one item matches. Sometimes you only need to know whether or not items match.includes

Same as indexOf, but searches in reverse.

const numbers = numbers.indexOf(2) //=> 1 numbers.indexOf(9) //=> -1. Takes an item (and optional start) and returns the Index or -1. const numbers = const isEven = number => number % 2 = 0 const isLessThanZero = number => number 1 numbers.findIndex(isLessThanZero) //=> -1. Takes a predicate and returns the Index or -1. const numbers = const isEven = number => number % 2 = 0 const isLessThanZero = number => number 2 numbers.find(isLessThanZero) //=> undefined Find The Index of Matching Item. Takes a predicate and returns the first matching item or undefined. everyĪlso searches for multiple items, see implementation below. const numbers = const isEven = number => number % 2 = 0 const isLessThanZero = number => number numbers.filter(isLessThanZero) //=>. Takes a predicate and returns an Array of all matching items. const isEven = number => number % 2 = 0 Searching for Multiple Items. The isEven function is an example of a predicate that takes a number and returns true if the number is even. A predicate is just a fancy word for a function that takes an item and returns a Boolean whether the item passes some condition.

Find method in javascript