@extra-array/flat-map/index.js

Flattens nested array, based on map function.

'use strict';
function id(v) {
    return v;
}
function is(v) {
    return Array.isArray(v);
}
function concat$(x, ...ys) {
    for (var y of ys)
        x.push(...y);
    return x;
}
function flatMap(x, fm = null, ft = null) {
    var fm = fm || id, ft = ft || is;
    var a = [], i = -1;
    for (var v of x) {
        var v1 = fm(v, ++i, x);
        if (ft(v1, i, x))
            concat$(a, v1);
        else
            a.push(v1);
    }
    return a;
}
module.exports = flatMap;