当前位置：网站首页>JS learning notes 09-12: prototype objects, foreach+tostring and recycle bin

JS learning notes 09-12: prototype objects, foreach+tostring and recycle bin

2022-07-19 08:30:00 【The man fished alone in the cold river snow】 

<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Document</title> <script> // // Define functions in global scope , Contaminates the namespace of the global scope   And it's not safe  // function Person(name,age,gender){
    
        //     this.name=name;
        //     this.age=age;
        //     this.gender=gender;
        // }
        // // Add... To the prototype sayName Method  // Person.prototype.sayName=function(){
    
        //     alert("Hello Hello everyone , I am a :"+this.name," Age is :"+this.age," The gender is :"+this.gender);
        // };

        // // Create a Person Example 
        // var per=new Person(" The Monkey King ",18," male ")
        // var per1=new Person(" Pig eight quit ",18," male ")
        // per.sayName();
        // per1.sayName();

        // Create a constructor  function MyClass() {
    

        }
        // towards MyClass Add a name attribute 
        MyClass.prototype.name = " I'm the name in the prototype ";
        var mc = new MyClass();
        mc.age=18;
        console.log(mc.name);
        // You can use the hasOwnProperty() To check whether the object itself contains the property 
        // When we use an object's properties or methods , Will now find in itself ,Object The prototype of the object is useless , If in Object Still not found in , Then return to undefined
        console.log(mc.hasOwnProperty("age"));


         
    </script>
</head>

<body>

</body>

</html>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        // Create an array 
        var arr=[" The Monkey King "," Pig eight quit "," The sand monk "," Tang's monk "," Bones jing "];

        /* forEach() Method requires a function as an argument   We create but not call , We call it a callback function   Passed in as an argument , We can define formal parameters , The browser will pass three parameters in the callback function   first ： The element being traversed , the second , Currently traversing the index of the element , Third   The array being traversed  */
        arr.forEach(function(value,index,obj){
    
            console.log(value,index,obj);
        });

    </script>
</head>
<body>
    
</body>
</html>

<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Document</title> <script> function Person(name, age, gender) {
    
            this.name = name;
            this.age = age;
            this.gender = gender;
        }

        // Create a Person example 
        var per = new Person(" The Monkey King ", 19, " male ");
        //  When we print an object directly on the page , Event is the output of the object toString() Return value of method 
        // If we want to output objects without output [object object], You can add a toString() Method 
        var result = per.toString();
        // Whether in prototype object 
        console.log(per.__proto__.__proto__.hasOwnProperty("toString"))


        // Garbage collection (GC)
        //  We need a garbage collection mechanism , To deal with the garbage generated in the process of program running 
        //  When an object has no variables or attributes to reference it , At this point we will never be able to manipulate the object , Too many objects take up a lot of space , Cause memory operation delay 
        //- stay JS There is an automatic garbage collection mechanism , There is no need to recycle 
        var obj=new Object();
        // Do various operations on objects ...  Set unused objects to null that will do 
        obj=null;



    </script>
</head>

<body>

</body>

</html>
原网站

版权声明
本文为[The man fished alone in the cold river snow]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/200/202207170727470068.html

边栏推荐

猜你喜欢

随机推荐