raf-schd

A throttle function that uses requestAnimationFrame to limit the rate at which a function is called.

For background information on rate limiting functions, see Rate limiting functions from scratch

1import rafSchd from 'raf-schd';
2
3const expensiveFn = arg => {
4  //...
5  console.log(arg);
6};
7
8const schedule = rafSchd(expensiveFn);
9
10schedule('foo');
11schedule('bar');
12schedule('baz');
13
14// animation frame fires
15
16// => 'baz'

Why?

raf-schd supports the use case where you want to limit the rate at which your functions are called based on requestAnimationFrame. Unlike a standard throttle function, raf-schd uses requestAnimationFrame to rate limit, rather than waiting a fixed amount of time. Using requestAnimationFrame for throttling is powerful because the browser will automatically reduce the amount of frames provided based on the available resources. So if the browser only provides 30fps then your throttled function will only be called 30 times.

raf-schd is an extremely useful performance utility.

Without raf-schd

Optimised scroll listener example taken from MDN

1var last_known_scroll_position = 0;
2var ticking = false;
3
4function doSomething(scroll_pos) {
5  // do something with the scroll position
6}
7
8window.addEventListener('scroll', function(e) {
9  last_known_scroll_position = window.scrollY;
10  if (!ticking) {
11    window.requestAnimationFrame(function() {
12      doSomething(last_known_scroll_position);
13      ticking = false;
14    });
15  }
16  ticking = true;
17});

With raf-schd

1import rafSchd from 'raf-schd';
2
3function doSomething(scroll_pos) {
4  // do something with the scroll position
5}
6
7const schedule = rafSchd(doSomething);
8
9window.addEventListener('scroll', function() {
10  schedule(window.scrollY);
11});

At the top level raf-schd accepts any function a returns a new ResultFn (a function that wraps your original function).

The ResultFn will execute your function with the latest arguments provided to it on the next animation frame.

Throttled with latest argument

1import rafSchd from 'raf-schd';
2
3const doSomething = () => {...};
4
5const schedule = rafSchd(doSomething);
6
7schedule(1, 2);
8schedule(3, 4);
9schedule(5, 6);
10
11// animation frame fires
12
13// do something called with => '5, 6'

Cancelling a frame with .cancel

raf-schd adds a .cancel property to the ResultFn so that it can be easily cancelled. The frame will only be cancelled if it has not yet executed.

1const schedule = rafSchd(doSomething);
2
3schedule('foo');
4
5schedule.cancel();
6
7// now doSomething will not be executed in the next animation frame

Types

rafSchedule

1type rafSchedule = (fn: Function) => ResultFn;
2
3// Adding a .cancel property to the WrapperFn
4
5type WrapperFn = (...arg: mixed[]) => void;
6type CancelFn = {|
7  cancel: () => void,
8|};
9type ResultFn = WrapperFn & CancelFn;

Testing your code

If you want to really ensure that your code is working how you intend it to - use raf-stub to test your animation frame logic.

Installation

1# yarn
2yarn add raf-schd
3
4# npm
5npm install raf-schd --save

Module usage

ES6 module

1import rafSchd from 'raf-schd';

CommonJS

If you are in a CommonJS environment (eg Node), then you will need add .default to your import:

1const rafSchd = require('raf-schd').default;