how to autoclose paranthesis in javascript input

1const closeChars = new Map([
2  ['{', '}'],
3  ['[', ']'],
4  ['(', ')']
5]);
6    
7maintextarea=document.getElementById('maintextarea');
8
9maintextarea.addEventListener('input', function (e) {
10
11    const pos = e.target.selectionStart;
12    const val = [...e.target.value];
13    
14    const char = val.slice(pos-1, pos)[0];
15    const closeChar = closeChars.get(char);
16    
17    if (closeChar) {
18      val.splice(pos, 0, closeChar);
19      e.target.value = val.join('');
20      e.target.selectionEnd = pos;
21    }
22});