initial code and an example

example/map.js

@@ -0,0 +1,6 @@
+var concatMap = require('../');
+var xs = [ 1, 2, 3, 4, 5, 6 ];
+var ys = concatMap(xs, function (x) {
+    return x % 2 ? [ x - 0.1, x, x + 0.1 ] : [];
+});
+console.dir(ys);

index.js

@@ -0,0 +1,9 @@
+module.exports = function (xs, fn) {
+    var res = [];
+    for (var i = 0; i < xs.length; i++) {
+        var x = fn(xs[i]);
+        if (Array.isArray(x)) res.push.apply(res, x);
+        else res.push(x);
+    }
+    return res;
+};