problems(js): add “2676. Throttle”

Signed-off-by: Matej Focko <me@mfocko.xyz>

problems/throttle.js

@@ -0,0 +1,35 @@
+/**
+ * @param {Function} fn
+ * @param {number} t
+ * @return {Function}
+ */
+var throttle = function(fn, t) {
+  let on_cooldown = false;
+  let queuedArgs = null;
+
+  const handler = () => {
+    if (queuedArgs === null) {
+      on_cooldown = false;
+      return;
+    }
+
+    fn.apply(null, queuedArgs);
+    queuedArgs = null;
+    on_cooldown = true;
+
+    setTimeout(handler, t);
+  };
+
+  return function(...args) {
+      queuedArgs = args;
+      if (!on_cooldown) {
+          handler();
+      }
+  }
+};
+
+/**
+ * const throttled = throttle(console.log, 100);
+ * throttled("log"); // logged immediately.
+ * throttled("log"); // logged at t=100ms.
+ */