## html代码
```
<html>
<head>
<meta charset="utf-8">
<script src="js/jquery-1.11.1.min.js" type="text/javascript"></script>
<title>文件上传</title>
</head>
<body>
<input id="good_img" name="good_img" class="weui-uploader__input" type="file" accept="image/*" multiple="">
<input type="hidden" id="imgBase64">
<button type="button" id="upload_btn">上传</button>
<div class="upload_div"></div>
</body>
</html>
```
## js代码
```
<script>
$('#upload_btn').click(function(){
var img = $('#imgBase64').val();
if (img) {
console.log(111);
}else{
alert('请选择上传图片');
}
})
//图片上传
$("#good_img").on('change',function(){
var filePath = $(this).val(), //获取到input的value，里面是文件的路径
fileFormat = filePath.substring(filePath.lastIndexOf(".")).toLowerCase(),
imgBase64 = '', //存储图片的imgBase64
fileObj = this.files[0]; //上传文件的对象,要这样写才行，用jquery写法获取不到对象
// 检查是否是图片
if( !fileFormat.match(/.png|.jpg|.jpeg/) ) {
alert('上传错误,文件格式必须为：png/jpg/jpeg');
return;
}
// 调用函数，对图片进行压缩
compress(fileObj,function(imgBase64){
imgBase64 = imgBase64; //存储转换的base64编码
$('#imgBase64').val(imgBase64);
var str='<img src="'+imgBase64+'"/>';
$(".upload_div").html(str);
});
});
// 不对图片进行压缩，直接转成base64
function directTurnIntoBase64(fileObj,callback){
var r = new FileReader();
// 转成base64
r.onload = function(){
//变成字符串
imgBase64 = r.result;
console.log(imgBase64);
callback(imgBase64);
}
r.readAsDataURL(fileObj); //转成Base64格式
}
// 对图片进行压缩
function compress(fileObj, callback) {
if ( typeof (FileReader) === 'undefined') {
console.log("当前浏览器内核不支持base64图标压缩");
//调用上传方式不压缩
directTurnIntoBase64(fileObj,callback);
}else if(fileObj.size<250000){ //图片小于250k就不压缩
console.log("不需要压缩");
directTurnIntoBase64(fileObj,callback);
} else {
try {
var reader = new FileReader();
reader.onload = function (e) {
var image = $('<img/>');
image.load(function(){
square = 700, //定义画布的大小，也就是图片压缩之后的像素
canvas = document.createElement('canvas'),
context = canvas.getContext('2d'),
imageWidth = 0, //压缩图片的大小
imageHeight = 0,
offsetX = 0,
offsetY = 0,
data = '';
canvas.width = this.width;
canvas.height = this.height;
context.clearRect(0, 0, square, square);
context.drawImage(this, 0, 0, this.width, this.height);
var data = canvas.toDataURL('image/jpeg');
//压缩完成执行回调
callback(data);
});
image.attr('src', e.target.result);
};
reader.readAsDataURL(fileObj);
}catch(e){
console.log("压缩失败!");
//调用直接上传方式 不压缩
directTurnIntoBase64(fileObj,callback);
}
}
}
</script>
```
