tricks/animation/timing.js

ES6 modules

// Timing function
import requestAnimationFrame from '../support/requestAnimationFrame.js';
import now from '../time/now.js';

const linear = t => t;

// Give a duration, an easing function and a frame callback we have...
export default (durationMS, easeFunc, frameCallback) => {

	if (!frameCallback) {
		// default to a linear easing function
		frameCallback = easeFunc;
		easeFunc = linear;
	}

	const start = now();

	tick(durationMS, easeFunc, frameCallback, start);
};


function tick(durationMS, easeFunc, frameCallback, start) {

	// what proportion through the animation is this?
	let t = (now() - start) / durationMS;

	if (t >= 1) {
		t = 1;
	}

	frameCallback(easeFunc(t), t);

	if (t < 1) {
		requestAnimationFrame(tick.bind(null, durationMS, easeFunc, frameCallback, start));
	}
}