Replace Full width bang to half width

Replace Full width bang! to half width!

// ==UserScript==
// @name    Replace Full width bang to half width
// @name:zh-CN   替换全角!到半角!
// @namespace https://github.com/fengkx/
// @match     https://duckduckgo.com/*
// @match     https://start.duckduckgo.com/*
// @version 0.1
// @description       Replace Full width bang! to half width!
// @description:en    Replace Full width bang! to half width!
// @description:zh    替换全角bang!到半角bang!
// @description:zh-CN 替换全角bang!到半角bang!
// @grant none
//@run-at             document-end
// ==/UserScript==

var $input = document.getElementById('search_form_input_homepage') || document.getElementById('search_form_input') ;
$input && $input.addEventListener('input', function (e) {
    if($input.value.search(/^!/) === 0) {
      var start = $input.selectionStart;
      var end = $input.selectionEnd;
      this.value = this.value.replace(/^!/, '!');
      $input.selectionStart=start;
      $input.selectionEnd=end;
    }
	
})