javascript如何求图形的面积

javascript求图形的面积的方法：【function Circle(r){ if(this instanceof Circle){ this.r=r; this.area=function(){ return Math.PI*this】。

本文操作环境：windows10系统、javascript 1.8.5、ThinkPad t480电脑。

图形面积求解：

第一种：构造函数

!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>
    

圆的面积：

!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>
    

输出的时候有两种形式：

Windows-普通函数

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

构造函数

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());
    

第二种：

!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>
    

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