var a = 3;
switch (a) {
  case 1:
    console.log(a);
    break;
  case 2:
  case 3:
    console.log(a);
    break;
  default:
    break;
}

var a = [4], b = '3';

function foo(a, b) {
  return Math.abs(a - b) < 2;
}

switch (true) {
  case !(a && b):  //过滤掉a,b其中有为‘假值'的情况
    console.log('a:'+a,' b:'+b);
    break;
  case foo(a,b):  //当a,b的差值在2以内，foo函数返回true
    console.log('a - b < '+Math.abs(a-b));
  case a == b:
    console.log(a+'=='+b);
    break;
  case a < b:
    console.log(a+'<'+b);
    break;
  case a > b:
    console.log(a+'>'+b);
    break;
  default:
    break;
}