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🌊 Smooth animation library for interpolating numbers
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Ola Β  test status gzip size dependencies npm install ola

Smooth animation library for inbetweening / interpolating numbers in realtime:

// Start tracking the value
const pos = Ola({ y: 0 });

// Set the value to update async
pos.set({ y: 100 });

// Read the evolution over time
setInterval(() => graph(pos.y), 5);

It works with multiple values/dimensions:

const pos = Ola({ x: 0, y: 0 });

window.addEventListener('click', e => {
  pos.set({ x: e.pageX, y: e.pageY });

setInterval(() => { = `${pos.x}px`; = `${pos.y}px`;
}, 10);

Also works great with many instances since they are independent:

// Generates 1000 instances seamlessly
const dots = Ola(Array(1000).fill(0));

// Everything updates every 600ms
setInterval(() => dots.forEach((dot, i) => {
  dots[i] = Math.random();
}), 600);

// ... read + paint screen here

Tip: click on the GIFs for a live demo with the code :)

Getting started

Install it with npm:

npm install ola

Then import it and use it:

import Ola from "ola";
const pos = Ola({ x: 0 });
console.log(pos.x); // 0

If you prefer to use a CDN:

<script src=""></script>
<script type="text/javascript">
  const pos = Ola({ x: 0 });
  console.log(pos.x); // 0


There are three distinct operations that can be run: creating an instance, setting it to update and reading it.

Create an instance

Ola(initial, time = 300);

The first parameter is the initial value. It can be either a single number, or an object of key:numbers or an array of numbers:

const heater = Ola(20); // Alias of `{ value: 20 }`
const motor = Ola({ angle: 180 }); // A named parameter for clarity
const position = Ola({ x: 0, y: 0 }); // Any number of properties
const heights = Ola([0, 0, 0, 0]); // A group of heights

The second parameter is how long the transition will last. It should be a number that represents the time in milliseconds:

const heater = Ola(20); // Default = 300 ms
const motor = Ola({ angle: 180 }, 1000); // Turn the motor slowly
const position = Ola({ x: 0, y: 0 }, 100); // Quick movements for the position
const heights = Ola([0, 0, 0, 0], 300); // 300, same as the default

Passing a single number as a parameter is the same as passing { value: num }, we are just helping by setting a shortname. It is offered for convenience, but recommend not mixing both styles in the same project.

It works with Javascript numbers, but please keep things reasonable (under Number.MAX_VALUE / 10):

console.log(Ola(1 / 100));

The time it takes to update can also be updated while setting the value, which will update it for any subsequent transition:

// All `pos.set()` will take 1 full second
const pos = Ola({ x: 0 }, 1000);
pos.set({ x: 100 }, 3000);

Update the value

heater.value = 25; // Since the constructor used a number, use `.value`
motor.angle = 90; // Turn -90 degrees from before
position.set({ x: 100, y: 100 }); // Move 0,0 => 100,100
heights[1] = 120; // Move the second (0-index) item to 120

When we update a property it is not updated instantaneously (that's the whole point of this library), but instead it's set to update asynchronously:

const pos = Ola({ x: 0 });
pos.set({ x: 100 });

// 0 - still hasn't updated

// 100 - after 300ms it's fully updated
setTimeout(() => console.log(pos.x), 1000);

Remember that if you set the value as Ola(10), this is really an alias for Ola({ value: 10 }), so use the property .value to update it:

heater.value = 25;
heater.set({ value: 25 });

You can see in this graph, the blue line is the value that is set though .set(), while the red line is the value that reading it returns:

Read the value

log(heater.value); // Since the constructor used a number, use `.value`
log(motor.angle); // Read as an object property
log(position.get("x")); // Find the X value
log(heights[1]); // Move the first item to 120

You can read the value at any time, and the value will be calculated at that moment in time:

const pos = Ola({ x: 0 });
pos.set({ x: 100 });

setInterval(() => {
  // It will update every time it's read
}, 10);

In contrast to other libraries, there's no need to tick/update the function every N ms or before reading the value, since Ola() uses math functions you should just read it when needed.


While there are some other great libraries like Tween, this one has some improvements:

Smooth in realtime

Other libraries don't move smoothly when there's an update while the previous transition is still ongoing. Ola makes sure there are no harsh corners:

Smooth interpolation with Ola() Harsh interpolation with Tweenmax

Status of libraries updating animation mid-way:

Lazy loading

Since this is driven by mathematical equations, the library doesn't calculate any value until it needs to be read/updated. It will also only change the one we need instead of all of the values:

const position = Ola({ x: 0, y: 0 });
position.x = 10; // Only updates X
console.log(position.x); // Calculates only X position, not y

Not only this is great for performance, but it also makes for a clean self-contained API where each instance is independent and portable.

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