单元练习题

"1"-9+"true"-parseInt(12.34)   // NaN
"9"-8+"false"   // 1false
"9"-8-"false"   // NaN
10+"2"-true-"false" // NaN
"10"+1-true  //100
"10"+1+true  //101true
"10"-1+true  // 10
"10"+true-1  // NaN
"true1"-1    // NaN

var a = 10
var m =a++ + ++a +20  // 10+12+20
console.log(m) // 42

var b = 4
var c = --b +10;  //13

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

var a = "abc" && 10   //10
var b = 0 && "abc"    //0

console.log(false == ""); // true
console.log(true == 1); // true
console.log(null == undefined);  // true
console.log(undefined == false);  // false
console.log(1 == "1"); // true
console.log(null == false); // false

• 1.1

  //下面那些符合命名规则
  var a%=20
  var 1a=20
  var _a=40;
  var $a=30   //最后两个
  

• 1.2

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

• 1.3

  var x = "2"+3+4;   // 234
  

• 1.4

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

• 1.5

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

• 1.6

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

• 1.7

  var x = 1;
  var y =x+x++;
  alert(y); // 2
  

• 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