html - In Javascript how can I set rgba without specifying the rgb?

Question

I have an HTML element whose background colour is set with rgba()

<div style="background-color: rgba(2,100,100,0);"> </div>

Then I have a timer that makes the background slowly fade in by changing the opacity value of the element in javascript

myEle.style.backgroundColor = "rgba(x,x,x,0.1)"; // I have to know the rgb values to update the alpha value

Is there a way to set the a value of rgba() without changing/knowing the rgb values?

Maybe I can do something like this?

var r = myEle.style.r;
var g = myEle.style.g;
var b = myEle.style.b;
myEle.style.backgroundColor = "rgba("+r+","+g+","+b+",0.1)";

Answer 1

You got the string, replace whatever
'rgba(1,1,1,0.3)'.replace(/[^,]+(?=))/, '0.5')