Kayode Oluwasegun
Debouncing in JavaScript

Debouncing in JavaScript

Kayode Oluwasegun's photo
Kayode Oluwasegun
·

2 min read

Imagine your web application makes requests to an API endpoint and each request has a price, debouncing the request operation may save you a great deal of money.

There are cases where you have long-running operations and these operations are in a position where they can be fired frequently by your application users. Such operations invoked continuously may affect the performance of your web application.

Debouncing is a technique that ensures long-running operations are not fired so often. It delays the execution of that particular program.

A common example is a search operation that is fired whenever a user types a query in an input field. Debouncing the operation would mean waiting for the user to stop typing for a particular time (usually milliseconds) before running the search operation.

Let’s write a simple implementation here:

function debounce(func, time = 300) {
  let timer;

  return (...args) => {
    clearTimeout(timer);
    timer = setTimeout(() => func.apply(this, args), time);
  };
}

Now we can create a mock project to see how this may function in a real application.

<!-- index.html -->
<html>
  <head>
    <title>Mock Search Page</title>
  </head>
  <body>
    <label for="search">Enter your search</label>
    <input id="search" type="text" name="search" />
    <script>
      const nameElement = document.querySelector("#search");

      function debounce(func, time = 500) {
        let timer;

        return (...args) => {
          clearTimeout(timer);
          timer = setTimeout(() => func.apply(this, args), time);
        };
      }

      const debouncedSearchFunction = debounce((event) => {
        console.log("querying: " + event.target.value + "....");
      });

      nameElement.addEventListener("keyup", (event) => {
        debouncedSearchFunction(event)
      });
    </script>
  </body>
</html>

In the code above, debounce returns a function and keeps a local variable timer (they both form a closure). timer acts like a state to manage the timing.

In the event listener callback, we call the function that is returned by debouce and, as we can see, the arguments in this function are passed to the func argument using the method [Function.prototype.apply](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/apply).

Conclusion

As I mentioned in the introduction of this article, in a case where each of your requests to an API endpoint is paid and the operations can be fired by the actions of a user. Debouncing the operations can be done to create a form of throughput per time (milliseconds).

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