在通常的登錄界面我們都可以看到驗(yàn)證碼，驗(yàn)證碼的作用是檢測(cè)是不是人在操作，防止機(jī)器等非人操作，防止數(shù)據(jù)庫(kù)被輕而易舉的攻破。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
canvas {
border: 1px solid red;
}
</style>
</head>
<body>
<canvas id="myCanvas" width="100" height="40">
您的瀏覽器不支持canvas
</canvas>
</body>
<script type="text/javascript">
var myCanvas = document.getElementById("myCanvas");
var context = myCanvas.getContext("2d");
//隨機(jī)字符（透明度）（大小隨機(jī)，位置隨機(jī)）；
var strStore = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
//隨機(jī)函數(shù)
function roundNum(min, max) {
return parseInt(Math.random() * (max - min) + min);
}
//文字內(nèi)容部分：
var str = "";
for(var i = 0; i < 5; i++) {
context.beginPath();
//隨機(jī)顏色（淺色：RGB - 200~250）
var color = `rgb(${roundNum(0,255)},${roundNum(0,255)},${roundNum(0,255)})`;
context.fillStyle = color;
context.font = roundNum(20,30)+"px Arial";
context.textAlign = "center";
str = strStore[roundNum(0,strStore.length)];
context.fillText(str, 10 + 18 * i, roundNum(20,35));
}
//10個(gè)左右的隨機(jī)（長(zhǎng)度隨機(jī)，位置隨機(jī)），干擾線
for(var j = 0; j < roundNum(5, 10); j++) {
context.beginPath();
var color = `rgb(${roundNum(0,255)},${roundNum(0,255)},${roundNum(0,255)})`;
context.strokeStyle = color;
context.moveTo(roundNum(0, 100), roundNum(0, 40));
context.lineTo(roundNum(0, 100), roundNum(0, 40));
context.stroke();
}
//干擾項(xiàng)：10個(gè)左右的隨機(jī)（半徑隨機(jī)，位置隨機(jī)），干擾圓
for(var j = 0; j < roundNum(5, 10); j++) {
context.beginPath();
context.fillStyle = color;
context.arc(roundNum(0, 100), roundNum(0, 40), roundNum(0, 5), Math.PI * 2 / (roundNum(1, 360)), Math.PI * 2 / (roundNum(1, 360)));
context.fill();
}
</script>
</html>
