JavaScript是一種廣泛使用的編程語言，它有一些被保留的關鍵字，這些關鍵字不能用作變量名或參數名。這些關鍵字在代碼中起著非常重要的作用，因此開發人員在編寫代碼時需要避免使用它們。

下面是 JavaScript 中的一些常見保留字：

abstract  boolean  break  byte  case  catch  char  class  const  continue
debugger  default  delete  do  double  else  enum  export  extends  false
final  finally  float  for  function  goto  if  implements  import  in
instanceof  int  interface  long  native  new  null  package  private  protected
public  return  short  static  super  switch  synchronized  this  throw  throws
transient  true  try  typeof  var  void  volatile  while  with  yield

我們可以使用下面的代碼來檢查我們的變量名是否是 JavaScript 中的保留字：

function checkReservedWord(variableName){
return JavascriptReservedWords.indexOf(variableName) !== -1;
}
const JavascriptReservedWords = [
"abstract","await",
"boolean","break","byte",
"case","catch","char",
"class","const","continue",
"debugger","default","delete",
"do","double","else",
"enum","export","extends",
"false","final","finally",
"float","for","function",
"if","implements","import",
"in","instanceof","int",
"interface","let","long",
"native","new","null",
"package","private","protected",
"public","return","short",
"static","super","switch",
"synchronized","this","throw",
"throws","transient","true",
"try","typeof","var",
"void","volatile","while",
"with","yield"
 ];

除了以上保留字，有些保留字只在嚴格模式下才會生效：

arguments  eval

在嚴格模式下，不能為函數實參指定arguments名稱，否則會拋出語法錯誤異常。eval也有一些限制，不能用作變量名或參數名。

總之，在編寫代碼時，確保不要使用 JavaScript 中的保留字作為變量名或參數名是非常重要的。否則，代碼將無法工作或會導致不可預測的結果。