initial commit

package.json

@@ -0,0 +1,11 @@
+{
+  "name": "promise-stream",
+  "version": "0.1.0",
+  "description": "a stream of updates connected with promises",
+  "main": "promise-stream.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "Jesse McDonald <nybble41@gmail.com>",
+  "license": "CC-PDDC"
+}

promise-stream.js

@@ -0,0 +1,72 @@
+(function(factory) {
+   if (typeof define !== 'undefined' && define.amd) {
+      define([], factory);
+   } else if (typeof define !== 'undefined' && define.petal) {
+      define(['promise-stream'], [], factory);
+   } else if (typeof module !== 'undefined' && module.exports) {
+      module.exports = factory();
+   } else {
+      window.PromiseStream = factory();
+   }
+})(function() {
+   class PromiseStream {
+      constructor() {
+         this._current = new Promise((resolve) => {
+            this._resolve = resolve;
+         });
+         this._next = this._current;
+         this._value = undefined;
+      }
+
+      get promise() {
+         /* waits for the _first_ update, or completes immediately */
+         return this._current;
+      }
+
+      get next_promise() {
+         /* waits for the _next_ update (which may be the first) */
+         return this._next;
+      }
+
+      get value() {
+         return this._value;
+      }
+
+      update(value) {
+         if (value !== undefined && value !== this._value) {
+            const resolve = this._resolve;
+            const current = this._next;
+            const next = new Promise((resolve) => {
+               this._resolve = resolve;
+            });
+
+            this._current = current;
+            this._next = next;
+            this._value = value;
+
+            resolve({ value, next });
+         }
+      }
+
+      once(cb) {
+         this.promise.then((v) => { cb(v.value); });
+      }
+
+      listen(cb) {
+         let cancelled = false;
+
+         function renew(v) {
+            if (!cancelled) {
+               cb(v.value);
+               v.next.then(renew);
+            }
+         }
+
+         this.promise.then(renew);
+
+         return () => { cancelled = true; };
+      }
+   }
+
+   return PromiseStream;
+});