Merge pull request #1337 from roblan/master

Added promiseDebounce

snippets/debouncePromise.md

@@ -0,0 +1,48 @@
+---
+title: debouncePromise
+tags: function,promise,advanced
+---
+
+Creates a debounced function that returns a promise, but delays invoking the provided function until at least `ms` milliseconds have elapsed since the last time it was invoked. 
+All promises returned during this time will return the same data.
+
+- Each time the debounced function is invoked, clear the current pending timeout with `clearTimeout()` and use `setTimeout()` to create a new timeout that delays invoking the function until at least `ms` milliseconds has elapsed.
+- Use `Function.prototype.apply()` to apply the `this` context to the function and provide the necessary arguments.
+- Create a new `Promise` and add its `resolve` and `reject` callbacks to the `pending` promises stack.
+- When `setTimeout` is called, copy the current stack (as it can change between the provided function call and its resolution), clear it and call the provided function.
+- When the provided function resolves/rejects, resolve/reject all promises in the stack (copied when the function was called) with the returned data.
+- Omit the second argument, `ms`, to set the timeout at a default of 0 ms.
+
+```js
+const debouncePromise = (fn, ms = 0) => {
+  let timeoutId;
+  const pending = [];
+  return (...args) =>
+    new Promise((res, rej) => {
+      clearTimeout(timeoutId);
+      timeoutId = setTimeout(() => {
+        const currentPending = [...pending];
+        pending.length = 0;
+        Promise.resolve(fn.apply(this, args)).then(
+          data => {
+            currentPending.forEach(({ resolve }) => resolve(data));
+          },
+          error => {
+            currentPending.forEach(({ reject }) => reject(error));
+          }
+        );
+      }, ms);
+      pending.push({ resolve: res, reject: rej });
+    });
+};
+```
+
+```js
+const fn = arg => new Promise(resolve => {
+  setTimeout(resolve, 1000, ['resolved', arg]);
+});
+const debounced = debouncePromise(fn, 200);
+debounced('foo').then(console.log);
+debounced('bar').then(console.log);
+// Will log ['resolved', 'bar'] both times
+```