2-1 例子

 var a  = "21"+4-true+"3"

var b  = 0 ||"abc";
var c = "abc" || 1;
var d = 0 || NaN;

var a = 10;
a++;   
b = ++a + 2;  
c = ++b + a++ + 4;
console.log(a);
console.log(b);
console.log(c);

• 1.1

  //下面那些符合命名规则
  var a%=20
  var 1a=20
  var _a=40;
  var $a=30

• 1.2

  console.log(""||"abc"); 
  console.log(0 == ''); 
  function b(){
  }
  console.log(typeof b);

• 1.3

  var x = "2"+3+4;

• 1.4

  var value = 0;
  if(value){
    console.log("true")
  }else{
    console.log("fasle")
  }

• 1.5

  var x=!false;
  var y;
  if(x==true){
    y = true
  }else{
    y = false
  }
  alert(y);

• 1.6

  var b = 10,c=3;
  if((b%c)>=2){
    alert("a")
  }else{
    alert("b")
  }

• 1.7

  var x = 1;
  var y =x+x++;
  alert(y);

• 1.8

  1.typeof能得到哪些类型
  2.===和==的区别

• 1.9JS中的内置对象

  Object,
  Array,
  Function,
  Number,
  String,
  Boolean,
  Date,
  RegExp,
  Error

• 1.10Boolean值有哪些情况为false

• 1.11

  100 == '100'
  0 == ''
  null == undefined