🟨JavaScript every() and some()

finding if all or at least one element of an array would meet a condition

Motivation

Suppose we have an array and we wish to go through its elements, then find out if all elements meet a condition, or at least one does so...

We could use the built-in every() and some() functions to iterate and test for existence:

// an array of names in a group
const names = ["Kenny", "Kyle", "Eric", "Butters"]

// find out if ALL the names have an "E" or "e"
const hasE = names.every((name) => name.toLowerCase().includes('e'))

console.log(hasE)
// true

// what if we don't use toLowerCase()?
const hasSmallE = names.every((name) => name.includes('e'))

console.log(hasSmallE)
// false

// find out if ANY of the names have a lowercase "e"
const eAnywhere = names.some((name) => name.includes('e'))

console.log(eAnywhere)
// true (Kenny, Kyle and Butters have a small "e")

Summary

So, both every() and some()

• return a simple boolean indicating

  • a uniformity (in the case of every()) or

  • an existence (in the case of some()) of a condition

• the condition in question appears in the body of the callback function

• that callback function gets passed into the parameter of the higher-order function, every() or some()