Add Throttling A Function Call as a javascript til.

README.md

@@ -45,6 +45,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 ## javascript
 
 - [Character Codes from Keyboard Listeners](javascript/character-codes-from-keyboard-listeners.md)
+- [Throttling A Function Call](javascript/throttling-a-function-call.md)
 - [Truthiness of Integer Arrays](javascript/truthiness-of-integer-arrays.md)
 
 ### postgres

javascript/throttling-a-function-call.md

@@ -0,0 +1,25 @@
+# Throttling A Function Call
+
+Imagine you have a JavaScript function that makes a request to your server.
+Perhaps it is sending user input from a `textarea` to be processed by the
+server. You may want to wrap this function in a keyboard event listener so
+that you are sure to react immediately to any user input. However, as the
+user starts typing away into this text area you may find that way to many
+requests are being fired off to the server. The request needs to be
+*throttled*.
+
+You can roll your own approach to sufficiently intermittent server calls.
+Though, it turns out that [underscore.js](http://underscorejs.org/) comes
+with two functions out of the box for this kind of behavior.
+
+- [`throttle`](http://underscorejs.org/#throttle) will give you function
+  that wraps your function in a way that essentially rate-limits it.
+
+- [`debounce`](http://underscorejs.org/#debounce), on the other hand, will
+  give you a function that only calls your function once `N` milliseconds
+  has passed since it was last called.
+
+These are two subtly different approaches to making sure a function gets
+call, just not too often.
+
+h/t [Jake Worth](https://twitter.com/jwworth)