彩虹小伞效果图如下：
代码如下：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>作业1</title>
<style>
#canvas {
position: absolute;
top: 0;
bottom: 0;
left: 0;
right: 0;
margin: 100px auto;
}
</style>
</head>
<body>
<canvas id="canvas" width="500" height="800"></canvas>
<script>
var canvas = document.getElementById("canvas");
var pen = canvas.getContext("2d");
// 彩虹七色小伞
var rainbow = ["#FF0000","#FF7F00","#FFFF00","#00FF00","#00FFFF","#0000FF","#871F78"]
for (var i = 0; i < 7; i++) {
pen.fillStyle = pen.strokeStyle = rainbow[i];
// 伞盖
pen.beginPath();
pen.arc(30 + 70 * i, 140, 30, Math.PI, 2 * Math.PI);
pen.closePath();
pen.fill();
// 伞柄
pen.beginPath();
pen.moveTo(30 + 70 * i, 140);
pen.lineTo(30 + 70 * i, 187);
pen.closePath();
pen.stroke();
// 伞把
pen.beginPath();
pen.arc(26 + 70 * i, 187, 4, 0, Math.PI);
pen.stroke();
}
// 随机变颜色的七个小伞
// setInterval(function () {
// for (var i = 0; i < 7; i++) {
// pen.fillStyle = pen.strokeStyle = randomColor();
// // 伞盖
// pen.beginPath();
// pen.arc(30 + 70 * i, 40, 30, Math.PI, 2 * Math.PI);
// pen.closePath();
// pen.fill();
// // 伞柄
// pen.beginPath();
// pen.moveTo(30 + 70 * i, 40);
// pen.lineTo(30 + 70 * i, 87);
// pen.closePath();
// pen.stroke();
// // 伞把
// pen.beginPath();
// pen.arc(26 + 70 * i, 87, 4, 0, Math.PI);
// pen.stroke();
// }
// }, 1000)
// 生成随机颜色的方法
function randomColor() {
var arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 'a', 'b', 'c', 'd', 'e', 'f']
var c = ''
for (var i = 0; i < 6; i++) {
c += arr[Math.round(Math.random() * 15)]
}
return "#" + c;
}
</script>
</body>
</html>