废话不多说了直接给大家介绍canvas实现手机端用来上传用户头像的代码，具体代码如下所示：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style>
label{
height:40px;
width:100px;
border:1px solid #666;
display:block;
text-align:center;
line-height:40px;
border-radius:10px;
background:lightgreen;
opacity: 1;
}
input{
display:none;
}
span{
display:block;
height:100%;
width:100%;
}
#canvas {
border:1px solid #666;
}
</style>
<script src="js/jquery-1.11.3.js"></script>
</head>
<body>
<label>
<input type="file" id="file" />
<span>上传文件</span>
</label>
<canvas width="300" height="300" id="canvas"></canvas>
</body>
<script>
$("#file").change(function (){
var file = new FileReader();//读取文件2进制
file.onload = function(e){
var base64 = e.target.result;
var img = new Image();//创建一个图片对象
img.onload = function (){
var canvas = $("#canvas").get(0);
var ctx = canvas.getContext("2d");
//使用drawImage显示图片
ctx.drawImage(img,0,0,canvas.width,canvas.height);
}
//把base64添加到图片上
img.src = base64;
};
file.readAsDataURL(this.files[0]);
});
</script>
</html>
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