My work

Exercises/1-callback.js

@@ -1,5 +1,15 @@
 'use strict';
 
-const iterate = (obj, callback) => null;
+const iterate = (obj, callback) => {
+  if (!obj) {
+    callback(new Error('obj needed'));
+    return;
+  }
+  for (const key of Object.keys(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 +1,19 @@
 'use strict';
 
-const contract = (fn, ...types) => null;
+const contract = (fn, ...types) => (...arr) => {
+  for (let i = 0; i < types.length - 1; i++) {
+    const argType = typeof arr[i];
+    const neededArgType = types[i].name.toLowerCase();
+    if (argType !== neededArgType) {
+      throw new TypeError('Types are different');
+    }
+  }
+  const neededReType = types[types.length - 1].name.toLowerCase();
+  const result = fn(...arr);
+  if (typeof result !== neededReType) {
+    throw new TypeError('Types are different');
+  }
+  return result;
+};
 
 module.exports = { contract };