Suprising replacement patterns in String.prototype.replace

console.js

const msg = 'This is a great message';

msg.replace('great', 'wonderful'); 
// "This is a wonderful message"
//
// -> 'great' is replaced by 'wonderful'

msg.replace('great', '$&-$&');
// "This is a great-great message"
// '$&' represents the matched substring
//
// -> 'great' is replaced by 'great-great'

msg.replace('great', '$`');
// "This is a This is a  message"
// '$`' represents the string before the matched string
//
// -> 'great' is replaced by 'This is a '

msg.replace('great', `$'`);
// "This is a  message message"
// `$'` represents the string after the matched string
//
// -> 'great' is replaced by ' message'