What is the easiest way to make a weighted random selection in JS? [duplicate]

I'm trying to make a program that will select a random element from an array, and want it to be that different elements have a different probability to be chosen. What is the best way to do this?

var char = ["a","b","c"];
var weights = ["0.2","0.3","0.5";
function randomSelection(){
     var randomchoice = ??;
     return randomchoice
}

Thanks!