<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>加载图片</title>
</head>
<body>
<canvas id="demo" width="400" height="400" style="border:1px solid red"></canvas>
<script type="text/javascript">
var canvas = document.getElementById("demo");
var cxt = canvas.getContext("2d");
function preImg(sourceId, targetId) {
cxt.clearRect(0, 0, 400, 400);
if (typeof FileReader === 'undefined') {
alert('Your browser does not support FileReader...');
return;
}
var reader = new FileReader();
reader.onload = function (e) {
var img = document.getElementById(targetId);
var cxt = document.getElementById("demo").getContext("2d")
img.src="https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=1557124323,393705227&fm=116&gp=0.jpg";
img.onload = function () {
cxt.drawImage(img, 0, 0);
}
}
reader.readAsDataURL(document.getElementById(sourceId).files[0]);
}
</script>
<input name="button" type="button" id="bt_display" onclick="preImg(sourceId, targetId)" value="图片一"/>
</body>
</html>