function filter(x, ft) // x: an iterable // ft: test function (v, i, x)

const xiterable = require('extra-iterable'); var x = [1, 2, 3, 4, 5]; [...xiterable.filter(x, v => v % 2 === 1)]; // → [1, 3, 5] [...xiterable.filter(x, v => v % 2 === 0)]; // → [2, 4]