problems(js): add “2629. Function Composition”

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/function-composition.js

@@ -0,0 +1,17 @@
+/**
+ * @param {Function[]} functions
+ * @return {Function}
+ */
+var compose = function(functions) {
+	return function(x) {
+        return functions.reduceRight(
+            (val, f) => f(val),
+            x,
+        );
+    };
+};
+
+/**
+ * const fn = compose([x => x + 1, x => 2 * x])
+ * fn(4) // 9
+ */