function hasPrefix(x, y, fc, fm) // x: an iterable // y: search prefix // fc: compare function (a, b) // fm: map function (v, i, x)

const xiterable = require('extra-iterable'); var x = [1, 2, 3, 4]; xiterable.hasPrefix(x, [1, 2]); // → true xiterable.hasPrefix(x, [-1, -2]); // → false xiterable.hasPrefix(x, [-1, -2], (a, b) => Math.abs(a) - Math.abs(b)); // → true xiterable.hasPrefix(x, [-1, -2], null, v => Math.abs(v)); // → true