switch(表达式) {
  case n:
  代码块
  break;
  case n:
  代码块
  break;
  default:
  默认代码块
}

switch (new Date().getDay()) {
 case 0:
  day = "星期天";
  break;
 case 1:
  day = "星期一";
   break;
 case 2:
  day = "星期二";
   break;
 case 3:
  day = "星期三";
   break;
 case 4:
  day = "星期四";
   break;
 case 5:
  day = "星期五";
   break;
 case 6:
  day = "星期六";
}

var a = 100;
var b = NaN;
switch (true) {
 case isNaN(a) || isNaN(b):
  console.log('NaNNaN');
  break;
 case a === b:
  console.log(0);
  break;
 case a < b:
  console.log(-1);
  break;
 default:
  console.log(1);
}

// NaNNaN

var Animal = 'Giraffe';
switch (Animal) {
 case 'Cow':
 case 'Giraffe':
 case 'Dog':
 case 'Pig':
  console.log('This animal will go on Noah\'s Ark.');
  break;
 case 'Dinosaur':
 default:
  console.log('This animal will not.');
}

// This animal will go on Noah's Ark.