When JavaScript executes the string replace method, there is a strange phenomenon about $.

Question

When replacing string replacement, if the new content is two consecutive $$, it will become 1 when output.

var str = '哈哈a哈哈a哈哈哈';
var re = str.replace('a','****');
console.log(re);
//结果是：哈哈****哈哈a哈哈哈
            
var str = '哈哈a哈哈a哈哈哈';
var re = str.replace('a','$$$$');
console.log(re);
//结果是：哈哈$$哈哈a哈哈哈
//4个$变成了2个，为什么

Answer 1

`
$ has special meaning in replace, just like for strings, the first transfer, $$ represents the character $
`