问如何确定字符串是否在JavaScript列表中？

Column IN ('a', 'b', 'c')

if (expression1 || expression2 || str === 'a' || str === 'b' || str === 'c') {
   // do something
}

if (expression1 || expression2 || {a:1, b:1, c:1}[str]) {
   // do something
}

var str = 'a',
   flag = false;

switch (str) {
   case 'a':
   case 'b':
   case 'c':
      flag = true;
   default:
}

if (expression1 || expression2 || flag) {
   // do something
}