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Method to calculate the circle area: 1. Create an input tag and receive the radius value; 2. Use "document.getElementById('id').value" to get the radius value in the input input box; 3. , use the area formula "area=3.14*(radius*radius)" to find the area of the circle.
The operating environment of this tutorial: Windows 7 system, JavaScript version 1.8.5, Dell G3 computer.
The specific condition is to enter a radius, then find the area, round to 2 decimal places,
<!DOCTYPE html>
<html lang="en"><head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
输入圆的半径：<input type="text" id="inp">
<input type="button" value="确定" onclick="test()">
</body>
</html>
<script>
function test(){
var inp = parseFloat(document.getElementById('inp').value);
var s = 3.14 * (inp * inp);
alert('面积为：' + s)
}
</script>[Recommended learning: javascript video tutorial]
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