why cannot the image appear in the web

Question

var url="https://www.sololearn.com/Icons/Courses/1024.png";
document.getElementById("background").style.backgroundImage="url(url)";

//while this way can show up.
document.getElementById("background").style.backgroundImage="url('https://www.sololearn.com/Icons/Courses/1024.png')";

Answer 1

Because in the first thing you posted the string is just "url(url)"

To replace the url with the actual value of the variable you have to do sometging like this:

"url(" + url + ")"