加权随机

// reusable function. Feed in an array and an ease and it'll return
// a function that pulls a random element from that array, weighted
// according to the ease you provide.
function weightedRandom(collection, ease) {
return gsap.utils.pipe(
	Math.random,            //random number between 0 and 1
	gsap.parseEase(ease),   //apply the ease
	gsap.utils.mapRange(0, 1, -0.5, collection.length-0.5), //map to the index range of the array, stretched by 0.5 each direction because we'll round and want to keep distribution (otherwise linear distribution would be center-weighted slightly)
	gsap.utils.snap(1),     //snap to the closest integer
	i => collection[i]      //return that element from the array
);
}

// usage:
var myArray = [0, 1, 2, 3],
getRandom = weightedRandom(myArray, "power4");

// now you can call it anytime and it'll pull a random element from myArray, weighted toward the end.
getRandom();
getRandom();
...