problems(js): add “2627. Debounce”

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

problems/debounce.js

@@ -0,0 +1,22 @@
+/**
+ * @param {Function} fn
+ * @param {number} t milliseconds
+ * @return {Function}
+ */
+var debounce = function(fn, t) {
+    let timeout = null;
+    return function(...args) {
+        clearTimeout(timeout);
+        timeout = setTimeout(() => {
+            timeout = null;
+            fn(...args);
+        }, t);
+    }
+};
+
+/**
+ * const log = debounce(console.log, 100);
+ * log('Hello'); // cancelled
+ * log('Hello'); // cancelled
+ * log('Hello'); // Logged at t=100ms
+ */