spring aims to aid in use cases where you have a value that you want to lerp towards 0.
spring(6); // 5
spring(6, 2); // 4
spring(-5); // -4
spring(-5, 4); // -1
var a = spring(10, 4); // 6
a = spring(a, 4); // 2
a = spring(a, 4); // -2
a = spring(a, 4); // 2