My work

Exercises/1-callback.js

@@ -1,5 +1,14 @@
 'use strict';
 
-const iterate = (obj, callback) => null;
+const iterate = (obj, callback) => {
+  if (!obj) {
+    callback(new Error('obj needed'));
+    return;
+  }
+  for (const key in obj) {
+    callback(key, obj[key], obj);
+  }
+  return;
+};
 
 module.exports = { iterate };

Exercises/2-closure.js

@@ -1,5 +1,6 @@
 'use strict';
 
-const store = x => null;
+const store = x => () => x;
 
 module.exports = { store };
+

Exercises/3-wrapper.js

@@ -1,5 +1,13 @@
 'use strict';
 
-const contract = (fn, ...types) => null;
+const contract = (fn, ...types) => (...arr) => {
+  for (let i = 1; i < types.length - 1; i++) {
+    if (typeof fn(...arr) !== types[i].name.toLowerCase()) {
+      throw new TypeError('Types are different');
+    }
+  }
+  return fn(...arr);
+};
 
 module.exports = { contract };
+