Q: Create Custom Easing using Javascript I am trying to create a custom easing function and I am experiencing a few difficulties. In other words, the maths is confusing me...
I would like my function to increment the width of a some elements within my page, and the increment value needs to decrease as the index of the element increases.
Consider these values:
50, 150, 230, 280, 310, 330

Whilst I appreciate it is likely to be impossible to generate these exact values, I essentially want a function that will come close to those values.
Here is what I have so far:
$('.something').each(function(i){
    var scale = Math.round(30*(i/10)*(2-(i/10)));
    dimension = scale*dimension;
    console.log(dimension);
});

This may be extremely easy but I am struggling to get my head around the maths today so any help would be much appreciated

A: Here's a live demo that shows how you can use a quadratic ease-out function to achieve a curve similar to the one you describe.


var out = document.getElementById("output");

// t: current time, b: beginning value, c: change in value, d: duration

function easeOutQuad(t, b, c, d) {
  return -c *(t/=d)*(t-2) + b;
}

for (var i = 0; i < 1; i+=0.1) {
  out.innerHTML += Math.round(easeOutQuad(i, 50, 280, 1)) + "<br>";
}
<div id="output"></div>


Shout-out to @c-smile for linking the jQuery easeOutQuad function in the comments, which this demo is based on.

A: You could look through the Easing Functions Generator by Robert Penner. It may be very useful for creating custom easing functions:
// generated example
function(t, b, c, d) {
    var ts=(t/=d)*t;
    var tc=ts*t;
    return b+c*(63.2425*tc*ts + -185.23*ts*ts + 198.58*tc + -93.89*ts + 18.2975*t);
};

