4月26日学习

if语句
- 练习
条件分支语句（switch）
while循环
for循环
break和continue
对象Object
- In 运算符
基本和引用数据类型
对象字面量
函数
函数的参数
函数的返回值
实参可以是任何值
立即调用
方法

if语句

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
  <script type="text/javascript">
      if(true){ 
        alert("success");
      }else if(){
        alert("idk");       
      }else{
          alert("flase");
      }
  </script>
    <title>测试</title>
</head>
<body>
</body>
</html>

练习

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
  <script type="text/javascript">
    var score = prompt("请输出期末成绩");
    if(score>100||score<0||isNaN(score)){
      alert("sorry");
    }else{
    if(score>=90){ 
        alert("nice");
      }else if(score>=60){
        alert("good");       
      }else{
          alert("bye");
      }
    }
  </script>
    <title>测试</title>
</head>
<body>
</body>
</html>

条件分支语句（switch）

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
  <script type="text/javascript">
           var num = 3;
    switch(num){
      case 1:
        console.log("1");
        break;
      case 2:
        console.log("2");
        break;
      case 3:
        console.log("3");
        break;
      default:
        console.log("error");
        break;
    }
  </script>
    <title>测试</title>
</head>
<body>
</body>
</html>

while循环

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
  <script type="text/javascript">
       var i = 0;    
    while(i<10){
      document.write(i);
      i++;
    }
  </script>
    <title>测试</title>
</head>
<body>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
  <script type="text/javascript">
       var i = 0;    
    do{
      document.write(i+"</br>");
      i++;
    }while(i<10);//先执行再判断
  </script>
    <title>测试</title>
</head>
<body>
</body>
</html>

for循环

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
  <script type="text/javascript">
       var i = 0;    
    for(;i<10;i++){
            document.write(i+"</br>");
    }
  </script>
    <title>测试</title>
</head>
<body>
</body>
</html>

break和continue

break跳出
continue跳过

对象Object
内建对象
宿主对象主要指由浏览器提供的对象比如BOM DOM

自定义对象

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
<script type="text/javascript">
     //创建对象
  //使用new关键字调用的函数，是构造函数，专门用来创建对象
  var obj = new Object();
  //添加属性 对象.属性名=属性值
  obj.name = "Tom";
  obj.age = 18;
  //读取对象中属性 对象.属性名
  console.log(obj.name);
  //修改就重新赋值
  //使用[]更加灵活
  obj[name] = "Tom";
  console.log(obj[name]);
</script>
  <title>测试</title>
</head>
<body>
</body>
</html>

js对象的属性值可以是任何数据类型也可以是对象

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
<script type="text/javascript">
  var obj = new Object();
  var obj2 = new Object();
  obj2[name] = "Tom";
  obj2[age] = "18";
  obj[test] = obj2;
  console.log(obj[test][name]);
</script>
  <title>测试</title>
</head>
<body>
</body>
</html>

In 运算符

该运算符可以检查一个对象中是否含有特定的属性
“属性名” in 对象

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
<script type="text/javascript">
  var obj = new Object();
  var obj2 = new Object();
  obj2[name] = "Tom";
  obj2[age] = "18";
  obj[test] = obj2;
  console.log("test" in obj);
</script>
  <title>测试</title>
</head>
<body>
</body>
</html>

基本和引用数据类型

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
<script type="text/javascript">
  var a =123;
  console.log("a ="+a);
  var obj = new Object();//基本数据类型为栈内存
  obj[name]="Tom";
  var obj2 = obj;
  obj[name]="Jack";
  console.log(obj[name]);//引用数据类型为堆内存,本质指针
  console.log(obj2[name]);//引用数据与基本的区别 obj与obj2都变了
  obj2=null;
  console.log(obj[name]);//相当于obj2对地址的指针断开了
  console.log(obj2[name]);//obj还是object obj2为空
  var obj3 = new Object();
  var obj4 = new Object();
  obj3[name]="Tom";
  obj4[name]="Tom";
  console.log(obj3[name] == obj4[name]);//false 双胞胎 指的地址不同
</script>
  <title>测试</title>
</head>
<body>
</body>
</html>

对象字面量

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
<script type="text/javascript">
  var obj = {}; //相当于var obj = new Object();
  var obj2 = {name:"Tom",age:18}; 
  var obj3 = {
    name:"Tom",
    age:18
    test:{name:"Jack"}
  }; 
</script>
  <title>测试</title>
</head>
<body>
</body>
</html>

函数

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
<script type="text/javascript">
  //函数也是对象
  var fun = new Function("console.log(1);");
  fun();//执行
  fun.hello="Hello";//也具有对象的功能
  console.log(fun.hello);
  //使用函数声明
  function    fun2(){
    console.log(1);
         console.log(2);
      console.log(3);
  }
  fun2();
  var fun3=function(){
    console.log(1);
  }
  fun3();
</script>
  <title>测试</title>
</head>
<body>
</body>
</html>

函数的参数

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
<script type="text/javascript">
  function sum(a,b){
          console.log(a+b);
  }
  sum(1,2);
  sum("1","hello");//调用函数是不会检查类型的
  sum(1,2,3);//调用函数是不会检查实参数量
  sum(1);//调用函数是不够那就是undefined
</script>
  <title>测试</title>
</head>
<body>
</body>
</html>

函数的返回值

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
<script type="text/javascript">
  function sum(a,b){
          var c =a+b;
        return c;
  }
  var result = sum(1,2);
</script>
  <title>测试</title>
</head>
<body>
</body>
</html>

return 直接结束整个函数

函数内部可以声明函数

实参可以是任何值

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
<script type="text/javascript">
  function isOu(num){
      if(num%2==0){
          return true;
    }else{
          return flase;
    }
  }
  var result = isOu(2);
  //创建对象
  //实参可以是个对象
  var obj={
    name:"Tom",
    age:"18",
    gender:"男"
  function sayHello(obj){
    console.log("我是"+obj.name);
    };
  sayHello(obj);
  //实参可以是函数
     function fun(a){
          a(obj);
  }
  fun(sayHello);
  function fun2(){
          function fun3(){
              alert(1);
      }
        return fun3;
  }
  fun2()();//相当于fun3()
  //fun3 与 fun3()不同
</script>
  <title>测试</title>
</head>
<body>
</body>
</html>

立即调用

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
<script type="text/javascript">
  //函数对象()
(function(){
  alert(1);
})();
</script>
  <title>测试</title>
</head>
<body>
</body>
</html>

方法

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
<script type="text/javascript">
  //对象的属性也可以是函数
  var obj = {};
  obj.name="Tom";
  obj.sayHello=function(){
          console.log(obj.name);
  };
  obj.sayHello();//调方法
  var obj2 = {
                  name:"猪八戒"，
                  age: 18,
                  sayName: function(){
                              console. log(obj2.name);
        }
  };
   //枚举对象中的属性
      obj2. sayName();
      var obj3 = {
                  name:"猪八戒"，
                  age: 18,
          gender:"男"
    };
     for(var n in obj){
    console.log(n);
    console.log(obj[n]);
  }//打印对象中的属性
</script>
  <title>测试</title>
</head>
<body>
</body>
</html>

if语句

练习

条件分支语句（switch）

while循环

for循环

break和continue

对象Object

In 运算符

基本和引用数据类型

对象字面量

函数

函数的参数

函数的返回值

实参可以是任何值

立即调用

方法