Adder implementation with closures

Author: tshemsedinov

JavaScript/8-adder.js

@@ -0,0 +1,10 @@
+'use strict';
+
+const adder = (a) => {
+  const value = () => a;
+  const add = (b) => adder(a + b);
+  return { add, value };
+};
+
+const v = adder(3).add(-9).add(12).value();
+console.log(v);

JavaScript/9-adder-on.js

@@ -0,0 +1,28 @@
+'use strict';
+
+const adder = (a) => {
+  let onZerro = null;
+  const obj = {};
+  const value = () => a;
+  const add = (b) => {
+    let x = a + b;
+    if (x < 0) {
+      x = 0;
+      if (onZerro) onZerro();
+    }
+    return adder(x);
+  };
+  const on = (name, callback) => {
+    if (name === 'zero') onZerro = callback;
+    return obj;
+  };
+  return Object.assign(obj, { add, value, on });
+};
+
+const a = adder(3)
+  .add(-9)
+  .on('zero', () => console.log('Less than zero'))
+  .add(12)
+  .add(5)
+  .value();
+console.log(a);