JavaScript is a commonly used web programming language that can be used to achieve a variety of interactive effects. This article will introduce how to use JavaScript to input the radius of a circle, and then calculate and output its area and circumference.
1. Enter the radius
Inputting the radius is the first step for us to calculate the circumference and area of a circle. This can be achieved with a simple HTML page. First, we need to create a text box and a button in an HTML file to enter the radius and start calculation. The code is as follows:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>求圆面积和周长</title>
</head>
<body>
<p>请输入圆的半径：</p>
<input type="number" id="radius"></input>
<button onclick="calculate()">计算</button>
<p id="area"></p>
<p id="circumference"></p>
<script src="circle.js"></script>
</body>
</html>This HTML page contains a text box and a calculation button, and also contains two A blank paragraph is used to output the results. Among them, the ID of the text box is "radius", which is used to obtain the radius input value. The button's onclick event is bound to a JavaScript function "calculate()", which is used to calculate the circumference and area of a circle. The results will be output in two paragraphs, represented by tags with IDs "area" and "circumference" respectively.
2. Calculate area and perimeter
In the HTML file, we introduced a JavaScript file named "circle.js". In this file we will write functions for calculating the area and circumference of a circle. The code is as follows:
function calculate() {
var radius = document.getElementById("radius").value;
// 计算面积
var area = Math.PI * Math.pow(radius, 2);
document.getElementById("area").innerHTML = "面积: " + area + "平方厘米";
// 计算周长
var circumference = 2 * Math.PI * radius;
document.getElementById("circumference").innerHTML = "周长: " + circumference + "厘米";
}This function has three main steps. First, it uses JavaScript's DOM methods to get the value of the text box, which is the radius of the circle entered by the user. It then calculates the area of the circle using the PI constant and the pow() function from the Math library. Finally, it calculates the circumference of the circle using the Math library and the entered radius, and outputs the results to two paragraphs in an HTML page. In this example, we're outputting the area and perimeter as strings, but you can format them as needed.
3. Testing and Expansion
We can now open the HTML file in the browser and start testing. Enter a value in the text box, then click the "Calculate" button, and the page will output the area and circumference of the circle. As shown in the figure below:
#You can try to change the input value and click the "Calculate" button multiple times to test the correctness of the calculation function. Additionally, you can extend this simple JavaScript program to accept and output other variables, or provide more complex interactive options to the user.
Conclusion
In this article, we introduced how to use JavaScript to enter the radius of a circle and calculate its area and circumference. JavaScript is a common tool for performing such interactive operations. It can easily manipulate HTML and other browser APIs, which makes writing web applications and web pages easier and more fun.
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