Composition task

Exercises/2-compose.js

@@ -1,5 +1,22 @@
 'use strict';
 
-const compose = (...fns) => x => null;
+const compose = (...fns) => {
+  let error = null;
+  try {
+    for (const fn of fns) {
+      if (!(fn instanceof Function)) throw new Error('Type of argument should be a function.');      
+    }
+  } catch (e) {
+    error = e;
+  }
+  const composed = x => {
+    if (error) return undefined;
+    return fns.reduceRight((v, f) => f(v), x);
+  }
+  composed.on = (eventName, callback) => {
+    if (eventName === 'error' && error) callback(error);
+  }
+  return composed;
+}
 
 module.exports = { compose };