练习A

var a = 10 && 20;
console.log(a);
var num = 20 || 30;
console.log(num);
var t = 0 || 20;
console.log(t);
var s = 0 && 30;
console.log(s);

 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);

1-2

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

1-3

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

1-4

var x = "2"+3+4;

1-5

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

1-6

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

1-7

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

1-8

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

1-9

1.typeof能得到哪些类型
2.===和==的区别

1-10 js中的内置对象

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

1-11 Boolean值有哪些情况下为false

1-12

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