Using Array.every()

The method Array.prototype.every() evaluates all elements in an array to see if they pass the test given by the provided function. If the array has no values the method returns true.

This is very useful when reducing an array to a boolean.

every((element) => {})
every((element, index) => {})
every((element, index, array) => {})

// TypeScript
every(predicate: (value: T, index: number, array: T[]) => unknown, thisArg?: any): boolean;

A common use of reduce and filter is to get a subset of items and then check if a condition is met. Instead, every can be used to check that condition directly.

// Before
const foo: boolean = [1, 2, 3].filter((n) => n > 2).length > 0
// Or
let foo: boolean = false
for (const n of [1, 2, 3]) {
  if (n > 2) {
    foo = false
  }
}

// After
const foo: boolean = [1, 2, 3].every((n) => n > 2)