If x+x has no overflow or underflow, is x+x-x always equals to x?

For example, when writing some formula, if I see something like:

x+x-x+...

(x+x-x is at the start) which if x+x has no overflow or underflow, is the result remains the same after simplifying to:

x+...

? Because I think x+x is just the exponent of the float number*2, but matissa remains unchanged, and x+x-x is just the exponent *2 and then /2, so I think it should be the same as x, but I’m not sure if it is correct.

Also I test some random numbers, which seems hold after running the following several times:

for(var i=0;i<1000;i++){
  var r=Math.random();
  if(r+r-r!=r){
    alert(r);
    break;
  }
}