Deferred implementation

Author: tshemsedinov

JavaScript/3-deferred.js

@@ -0,0 +1,69 @@
+'use strict';
+
+const DEFERRED_PENDING = 0;
+const DEFERRED_RESOLVED = 1;
+const DEFERRED_REJECTED = 2;
+
+const deferred = () => ({
+  value: undefined,
+  onDone: null,
+  onFail: null,
+  status: DEFERRED_PENDING,
+  isPending() {
+    return this.status === DEFERRED_PENDING;
+  },
+  isResolved() {
+    return this.status === DEFERRED_RESOLVED;
+  },
+  isRejected() {
+    return this.status === DEFERRED_REJECTED;
+  },
+  done(callback) {
+    this.onDone = callback;
+    if (this.isResolved()) callback(this.value);
+    return this;
+  },
+  fail(callback) {
+    this.onFail = callback;
+    if (this.isRejected()) callback(this.value);
+    return this;
+  },
+  resolve(value) {
+    this.value = value;
+    if (this.onDone) this.onDone(value);
+    return this;
+  },
+  reject(value) {
+    this.value = value;
+    if (this.onFail) this.onFail(value);
+    return this;
+  }
+});
+
+// Usage
+
+const persons = {
+  10: 'Marcus Aurelius',
+  11: 'Mao Zedong',
+  12: 'Rene Descartes',
+};
+
+const getPerson = id => {
+  const result = deferred();
+  setTimeout(() => {
+    const name = persons[id];
+    if (name) result.resolve({ id, name });
+    else result.reject(new Error('Person is not found'));
+  }, 1000);
+  return result;
+};
+
+const d1 = getPerson(10)
+  .done(value => console.log('Resolved d1', value))
+  .fail(error => console.log('Resolved d1', error));
+console.dir({ d1 });
+
+const d2 = getPerson(20)
+  .done(value => console.log('Resolved d2', value))
+  .fail(error => console.log('Resolved d2', error.message));
+console.dir({ d2 });