javascript从image转换为base64位编码的String

最近需要把app的微信分享方法开放给webview，涉及到分享的图片，如果通过传送图片连接，那将要在后台再取一次图片文件，会影响速度，我选择webview把image以base64位编码的方式传给本地应用。 下面是实现的参考代码：

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<title>Image to Base64 - jsFiddle demo by handtrix</title> 

<script type='text/javascript' src='//code.jquery.com/jquery-2.0.2.js'></script> 

<link rel="stylesheet" type="text/css" href="/css/result-light.css" rel="external nofollow" > 

<style type='text/css'>
@import url('//netdna.bootstrapcdn.com/bootstrap/3.1.0/css/bootstrap.min.css'); 

body{
padding: 20px;
}
</style> 

<script type='text/javascript'>//<![CDATA[
$(window).load(function(){
/**
* convertImgToBase64
* @param {String} url
* @param {Function} callback
* @param {String} [outputFormat='image/png']
* @author HaNdTriX
* @example
convertImgToBase64('http://goo.gl/AOxHAL', function(base64Img){
console.log('IMAGE:',base64Img);
})
*/
function convertImgToBase64(url, callback, outputFormat){
var canvas = document.createElement('CANVAS');
var ctx = canvas.getContext('2d');
var img = new Image;
img.crossOrigin = 'Anonymous';
img.onload = function(){
canvas.height = img.height;
canvas.width = img.width;
ctx.drawImage(img,0,0);
var dataURL = canvas.toDataURL(outputFormat || 'image/png');
callback.call(this, dataURL);
// Clean up
canvas = null;
};
img.src = url;
} 

$('#img2b64').submit(function(event){
var imageUrl = $(this).find('input[name=url]').val();
console.log('imageUrl', imageUrl);
convertImgToBase64(imageUrl, function(base64Img){
$('.output')
.find('textarea')
.val(base64Img)
.end()
.find('a')
.attr('href', base64Img)
.text(base64Img)
.end()
.find('img')
.attr('src', base64Img);
}); 

event.preventDefault();
}); 

});//]]> 

</script>
</head>
<body>
<h2>Input</h2>
<form class="input-group" id="img2b64">
<input
type="url"
name="url"
class="form-control"
placeholder="Insert an IMAGE-URL"
value="http://upload.wikimedia.org/wikipedia/commons/4/4a/Logo_2013_Google.png"
required>
<span class="input-group-btn">
<input
type="submit"
class="btn btn-default">
</span>
</form>
<hr>
<h2>Output</h2>
<div class="output">
<textarea class="form-control"></textarea><br>
<a></a><br><br>
<img><br>
</div>
</body>
</html>

PS：这里再为大家提供一款在线图片转base64编码的工具供大家参考使用：

图片转换为Base64编码在线工具：http://tools.jb51.net/transcoding/img2base64