[рони]

veltony,

function escapeRegExp(string){
  return string.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
}

var string = "abbb ccc";
var a = "Abbb";
var reg = new RegExp(escapeRegExp(a),"i");
string = string.replace(reg, "");
alert(string);