所属分类：web前端开发
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
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<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>推荐学习：javascript视频教程
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