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How to find the area of a graphic in javascript

王林Original: 2021-10-26 16:21:042664browse

Javascript method to find the area of a graphic: [function Circle(r){ if(this instanceof Circle){this.r=r; this.area=function(){return Math.PI*this].

#The operating environment of this article: windows10 system, javascript 1.8.5, thinkpad t480 computer.

Graphic area solution:

The first type: constructor

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        function Retangle(a,b){
            if(this instanceof Retangle){
                this.a=a;
                this.b=b;
                this.area=function(){
                    return this.a*this.b;
                    //console.log(Math.PI*this.r*this.r);
                }
                this.premeter=function(){
                    return (this.a+this.b)*2;
                    //console.log(Math.PI*this.r*2);
                }
            }else{
                return new Retangle(a,b);
            }
        }
        let c=new Retangle(10,10);
        //console.log(c instanceof Circle);//判断bool值
        console.log(c.area());
        console.log(c.premeter());
        Retangle(10,10);
    </script>
</head>
<body>
</body>
</html>

The area of the circle:

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        function Circle(r){
            if(this instanceof Circle){
                this.r=r;
                this.area=function(){
                    return Math.PI*this.r*this.r;
                }
                this.premeter=function(){
                    return Math.PI*this.r*2;
                }
            }else{
                return new Circle(r);
            }
        }
        let c=new Circle(10);
        //console.log(c instanceof Circle);
        console.log(c.area());
        console.log(c.premeter());
        Circle(10);
    </script>
</head>
<body>
 
</body>
</html>

There are two forms of output:

Windows-Common function

Circle(10);
console.log(window.r);
console.log(window.area());
console.log(window.premter());

Constructor

let c = new Circle(10);
// console.log(c);
console.log(c instanceof Circle);
 
console.log(c.r);
console.log(c.area());
console.log(c.premter());

Second type:

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        function Retangle(){
            var a = document.getElementById("a1").value;
            var b = document.getElementById("b1").value;
            alert("矩形面积："+a*b);
        }
    </script>
</head>
<body>
<form>
    长：<br>
    <input type="text" id="a1"><br>
    宽：<br>
    <input type="text" id="b1"><br>
    <button onclick="Retangle()" name="矩形面积" value="">计算面积</button>
    <input type="reset" name="reset" value="重置">
</form>
</body>
</html>

Recommended learning:javascript video tutorial

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