"Uncaught TypeError: Object #<an HTMLElement> has no method 'replace'"

I have a string like "1,000"
I want to take out the "," and I use in the contentscript this code

var something;
something = document.getElementById('else');
something = something.replace(",","");

document.getElementById('whatever').appendChild(something);

You have a basic JavaScript DOM API error here.
This is not a JavaScript learning group. Please, next time, search for
answers through a general search engine (if it also does not work within a
regular web page\JavaScript, then it must be unrelated to extensions).

You are trying to call the "replace" method of a DOM element. Only strings
(or special\user defined objects) have that "replace" method.
This is the right code -
var something = document.getElementById('else');
something.textContent = something.textContent.replace(",", "");

(No need to append it, it will change the element with this code already.)

☆*PhistucK*