JSPM

iterable.interpolate(x, fn);
// x:  an iterable
// fn: combine function (a, b)

const array = require('extra-array');

var x = [1, 2, 3];
array.interpolate(x, (a, b) => (a + b)/2);
// [ 1, 1.5, 2, 2.5, 3 ]